Magnetic tape having characterized magnetic layer

ABSTRACT

A magnetic tape is provided in which the total thickness of the non-magnetic layer and the magnetic layer is equal to or smaller than 0.60 μm. The magnetic layer includes ferromagnetic hexagonal ferrite powder and an abrasive. The percentage of a plan view maximum area of the abrasive confirmed in a region having a size of 4.3 μm×6.3 μm of the surface of the magnetic layer by plane observation using a scanning electron microscope, with respect to the total area of the region, is equal to or greater than 0.02% and less than 0.06%. Further, the tilt cos θ of the ferromagnetic hexagonal ferrite powder with respect to a surface of the magnetic layer acquired by cross section observation performed by using a scanning transmission electron microscope is 0.85 to 1.00.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2016-169851 filed on Aug. 31, 2016. The aboveapplication is hereby expressly incorporated by reference, in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for datastorage such as data back-up. The recording and/or reproducing ofsignals to the magnetic tape are normally performed by mounting amagnetic tape cartridge including the magnetic tape on a drive, allowingthe magnetic tape to run in the drive, and bringing the surface of themagnetic tape (surface of a magnetic layer) to come into contact with amagnetic head to slide thereon. Hereinafter, the magnetic tape is simplyreferred to as a “tape” and the magnetic head is also simply referred toas a “head”.

For example, in order to continuously or intermittently repeatedlyreproduce the signal recorded in the magnetic tape, repeated running ofthe magnetic tape is performed in the drive (hereinafter, also simplyreferred to as “repeated running”). It is desired that a deteriorationof electromagnetic conversion characteristics during such repeatedrunning is prevented, from a viewpoint of increasing reliability of themagnetic tape for data storage use. This is because a magnetic tape, inwhich electromagnetic conversion characteristics during the repeatedrunning are hardly deteriorated, can continuously exhibit excellentelectromagnetic conversion characteristics, even when the running iscontinuously or intermittently repeated in a drive.

As a reason of a deterioration of electromagnetic conversioncharacteristics due to the repeated running, occurrence of a phenomenon(called a “spacing loss”) in which a distance between a surface of amagnetic layer and a head is widened, is exemplified. As a reason ofthis spacing loss, attachment of foreign materials derived from a tapeto a head, while a surface of a magnetic layer and a head continue thesliding during the repeated running, that is, generation of headattached materials is exemplified. In the related art, as a measureagainst the generation of the head attached materials, an abrasive hasbeen included in the magnetic layer, in order to impart a function ofremoving the head attached materials to the surface of the magneticlayer (for example, see JP2014-179149A). Hereinafter, the function ofthe surface of the magnetic layer of removing the head attachedmaterials is referred to as “abrasion properties of the surface of themagnetic layer” or simply “abrasion properties”.

SUMMARY OF THE INVENTION

JP2014-179149A discloses that a magnetic tape disclosed inJP2014-179149A can exhibit excellent electromagnetic conversioncharacteristics. In order to increase reliability of such a magnetictape capable of exhibiting excellent electromagnetic conversioncharacteristics, for use of data storage, it is desired that adeterioration of electromagnetic conversion characteristics during therepeated running is prevented. Therefore, the inventor has madeintensive research in order to find means for preventing a deteriorationof electromagnetic conversion characteristics during the repeatedrunning of the magnetic tape. From such research, the inventor hasfocused that, not only generation of head attached materials is a reasonof spacing loss, but also partial chipping of a head can be a reason ofspacing loss. Specific description is as follows. By increasing abrasionproperties of a surface of a magnetic layer, the spacing loss caused bythe head attached materials can be reduced. However, as abrasionproperties of the surface of the magnetic layer increase, the headeasily partially chips due to the sliding between the surface of themagnetic layer and the head. In a case where partial chipping of thehead occurs, a distance between the surface of the magnetic layer andthe head in the chipped portion is widened. This may also be a reason ofthe spacing loss.

In regards to abrasion properties of the surface of the magnetic layer,as disclosed in JP2014-179149A, as an abrasive is present in themagnetic layer in a fine state, abrasion properties tend to bedeteriorated. The partial chipping of the head can be prevented by thedeterioration of the abrasion properties, but the head attachedmaterials are hardly removed. As described above, the removal of thehead attached materials and the partial chipping of the head are in arelationship of the tradeoff.

Meanwhile, in order to increase recording capacity for 1 reel of amagnetic tape cartridge, it is desired to increase the total length ofthe magnetic tape accommodated in 1 reel of the magnetic tape cartridgeby decreasing the total thickness of the magnetic tape (that is,thinning the magnetic tape). As one method of thinning the magnetictape, a method of decreasing the total thickness of a non-magnetic layerand a magnetic layer of a magnetic tape including the non-magnetic layerand the magnetic layer on a non-magnetic support in this order is used.However, in such studies of the inventor, it was clear that, it wasdifficult to overcome the relationship of the tradeoff to prevent adeterioration of electromagnetic conversion characteristics during therepeated running in a low temperature and high humidity environment, ina magnetic tape having a decreased total thickness of a non-magneticlayer and a magnetic layer which is equal to or smaller than 0.60 μm,compared to a magnetic tape having the total thickness of a non-magneticlayer and a magnetic layer which exceeds 0.60 μm. Hereinafter, thedeterioration of electromagnetic conversion characteristics indicates adeterioration of electromagnetic conversion characteristics in a lowtemperature and high humidity environment, unless otherwise noted. Thelow temperature and high humidity environment can be, for example, anenvironment in which an atmosphere temperature is 10° C. to 20° C. and arelative humidity is 70% to 90%. The magnetic tape may also be used inthe low temperature and high humidity environment, and therefore, it isdesired that a deterioration of electromagnetic conversioncharacteristics during the repeated running is prevented in such anenvironment.

Therefore, an object of the invention is to provide a magnetic tapewhich has the total thickness of a non-magnetic layer and a magneticlayer equal to or smaller than 0.60 μm and in which electromagneticconversion characteristics are hardly deteriorated, even when therunning is repeated in a low temperature and high humidity environment.

According to one aspect of the invention, there is provided a magnetictape comprising: a non-magnetic support; a non-magnetic layer includingnon-magnetic powder and a binding agent on the non-magnetic support; anda magnetic layer including ferromagnetic powder and a binding agent onthe non-magnetic layer, in which the total thickness of the non-magneticlayer and the magnetic layer is equal to or smaller than 0.60 μm, theferromagnetic powder is ferromagnetic hexagonal ferrite powder, themagnetic layer includes an abrasive, a percentage of a plan view maximumarea of the abrasive confirmed in a region having a size of 4.3 μm×6.3μm of the surface of the magnetic layer by plane observation using ascanning electron microscope, with respect to the total area of theregion is equal to or greater than 0.02% and less than 0.06%, and a tiltcos θ (hereinafter, also simply referred to as a “cos θ”) of theferromagnetic hexagonal ferrite powder with respect to a surface of themagnetic layer acquired by cross section observation performed by usinga scanning transmission electron microscope is 0.85 to 1.00.

In one aspect, a Brunauer-Emmett-Teller (BET) specific surface area ofthe abrasive is in a range of 14 to 40 m²/g. The BET specific surfacearea is a specific surface area measured by a BET method regardingprimary particles.

In one aspect, the abrasive is alumina powder.

In one aspect, the cos θ is 0.89 to 1.00.

In one aspect, the cos θ is 0.95 to 1.00.

In one aspect, the magnetic layer includes a polyester chain-containingcompound having a weight-average molecular weight of 1,000 to 80,000.

In one aspect, an activation volume of the ferromagnetic hexagonalferrite powder is 800 nm³ to 2,500 nm³.

In one aspect, the percentage of a plan view maximum area of theabrasive confirmed in a region having a size of 4.3 μm×6.3 μm of thesurface of the magnetic layer by plane observation using a scanningelectron microscope, with respect to the total area of the region is0.02% to 0.05%.

In one aspect, the total thickness of the non-magnetic layer and themagnetic layer is 0.20 μm to 0.60 μm.

In one aspect, the magnetic layer includes an aromatic hydrocarboncompound including a phenolic hydroxyl group.

In one aspect, the ferromagnetic hexagonal ferrite powder includes Al.

According to one aspect of the invention, it is possible to provide amagnetic tape which has the total thickness of a non-magnetic layer anda magnetic layer equal to or smaller than 0.60 μm and in whichelectromagnetic conversion characteristics during the repeated runningare hardly deteriorated in a low temperature and high humidityenvironment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram of an angle θ regarding a cos θ.

FIG. 2 is an explanatory diagram of another angle θ regarding a cos θ.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to one aspect of the invention, there is provided a magnetictape including: a non-magnetic support; a non-magnetic layer includingnon-magnetic powder and a binding agent on the non-magnetic support; anda magnetic layer including ferromagnetic powder and a binding agent onthe non-magnetic layer, in which the total thickness of the non-magneticlayer and the magnetic layer is equal to or smaller than 0.60 μm, theferromagnetic powder is ferromagnetic hexagonal ferrite powder, themagnetic layer includes an abrasive, a percentage of a plan view maximumarea of the abrasive confirmed in a region having a size of 4.3 μm×6.3μm of the surface of the magnetic layer by plane observation using ascanning electron microscope, with respect to the total area of theregion is equal to or greater than 0.02% and less than 0.06%, and a tiltcos θ of the ferromagnetic hexagonal ferrite powder with respect to asurface of the magnetic layer acquired by cross section observationperformed by using a scanning transmission electron microscope is 0.85to 1.00.

The following description contains surmise of the inventor. Theinvention is not limited by such surmise.

The surmise of the inventor regarding the magnetic tape is as follows.

(1) As described above, it was clear that, it was difficult to prevent adeterioration of electromagnetic conversion characteristics during therepeated running in a low temperature and high humidity environment, ina magnetic tape having a decreased total thickness of a non-magneticlayer and a magnetic layer which is equal to or smaller than 0.60 μm,compared to a magnetic tape having the total thickness of a non-magneticlayer and a magnetic layer which exceeds 0.60 μm. The reason thereof maybe a change of a contact state between the surface of the magnetic layerand the head due to a decrease of only the total thickness of thenon-magnetic layer and the magnetic layer. Due to such a change of thecontact state, the inventor has surmised that a phenomenon that the headeasily partially chips due to the abrasive present in the magnetic layermay be one of the reasons of the spacing loss. In regards to this point,the inventor has considered that a state of the abrasive present in themagnetic layer which is in a state satisfying a percentage which will bedescribed later in detail, indicates that the abrasive is present in themagnetic layer in a fine state. The inventor has surmised that thiscontributes to the prevention of partial chipping of the head during therepeated running.

(2) However, when the abrasive is only simply present in the magneticlayer in a fine state, abrasion properties of the surface of themagnetic layer are deteriorated. That is, a function of removing headattached materials by the surface of the magnetic layer is deteriorated.In regards to this point, the inventor has considered that, theferromagnetic hexagonal ferrite powder present in the magnetic layer ina state where the cos θ is in the range described above, contributes tothe preventing of the abrasive present in the vicinity of the surface ofthe magnetic layer from being pressed into the magnetic layer at thetime of the sliding between the surface of the magnetic layer and thehead. Accordingly, the inventor has surmised that, even in a case wherethe abrasive is present in the magnetic layer in a fine state, it ispossible to exhibit an excellent function of removing head attachedmaterials by the abrasive. Specific descriptions will be describedlater.

The inventor has surmised that, as a result of reducing the spacing lossby satisfying both of the prevention of partial chipping of the head andthe removal of the head attached materials as described above, it ispossible to prevent a deterioration of electromagnetic conversioncharacteristics during the repeated running in the magnetic tape havinga decreased total thickness of the non-magnetic layer and the magneticlayer which is equal to or smaller than 0.60 μm.

However, the invention is not limited to the surmises described above.

Hereinafter, the magnetic tape will be described more specifically.

In the invention and the specification, the “surface of the magneticlayer” is identical to the surface of the magnetic tape on the magneticlayer side. In the invention and the specification, the “ferromagnetichexagonal ferrite powder” means an aggregate of a plurality offerromagnetic hexagonal ferrite particles. Hereinafter, particles(ferromagnetic hexagonal ferrite particles) configuring theferromagnetic hexagonal ferrite powder are also referred to as“hexagonal ferrite particles” or simply “particles”. The “aggregate” notonly includes an aspect in which particles configuring the aggregatedirectly come into contact with each other, but also includes an aspectin which a binding agent, an additive, or the like is interposed betweenthe particles. The points described above are also applied to variouspowder forms such as non-magnetic powder of the invention and thespecification, in the same manner.

Total Thickness of Non-Magnetic Layer and Magnetic Layer

The total thickness of the non-magnetic layer and the magnetic layer ofthe magnetic tape is equal to or smaller than 0.60 μm and preferablyequal to or smaller than 0.50 μm, from a viewpoint of thinning themagnetic tape. In addition, the total thickness of the non-magneticlayer and the magnetic layer is, for example, equal to or greater than0.10 μm or equal to or greater than 0.20 μm.

Various thicknesses such as a thickness of the non-magnetic layer and athickness of the magnetic layer will be described later in detail. Thethicknesses of various layers of the magnetic tape and the non-magneticsupport can be acquired by a well-known film thickness measurementmethod. As an example, a cross section of the magnetic tape in athickness direction is, for example, exposed by a well-known method ofion beams or microtome, and the exposed cross section is observed with ascanning electron microscope. In the cross section observation, variousthicknesses can be acquired as a thickness acquired at one position ofthe cross section in the thickness direction, or an arithmetical mean ofthicknesses acquired at a plurality of positions of two or morepositions, for example, two positions which are arbitrarily extracted.In addition, the thickness of each layer may be acquired as a designedthickness calculated according to the manufacturing conditions.

State of Abrasive Present in Magnetic Layer

The magnetic tape includes an abrasive in the magnetic layer. Theabrasive is present in the magnetic layer in a state where a percentageof a plan view maximum area of the abrasive confirmed in a region havinga size of 4.3 μm×6.3 μm of the surface of the magnetic layer by planeobservation using a scanning electron microscope (SEM), with respect tothe total area (100%) of the region is equal to or greater than 0.02%and less than 0.06%. The inventor has surmised that the abrasive presentin the magnetic layer in a state where the percentage of the plan viewmaximum area of the abrasive with respect to the total area of theregion (hereinafter, also referred to as a “plan view maximum areapercentage of the abrasive” or simply a “percentage”) is equal to orgreater than 0.02% contributes to the removal of the head attachedmaterials, and the abrasive present in the magnetic layer in a statewhere the percentage is less than 0.06% contributes to the prevention ofpartial chipping of the head. Accordingly, the inventor has surmisedthat, the prevention of occurrence of spacing loss contributes to theprevention of a deterioration of electromagnetic conversioncharacteristics during the repeated running in a low temperature andhigh humidity environment. The percentage is preferably 0.02% to 0.05%and more preferably 0.02% to 0.04%.

As a result of the intensive studies of the inventor, it was clear that,in the magnetic tape having the total thickness of the non-magneticlayer and the magnetic layer equal to or smaller than 0.60 μm, inaddition to allowing the abrasive to be present in the magnetic layer ina state where the percentage is equal to or greater than 0.02% and lessthan 0.06%, allowing the ferromagnetic hexagonal ferrite powder to bepresent in the magnetic layer in a state where the cos θ is 0.85 to 1.00also contributes to the prevention of a deterioration of electromagneticconversion characteristics during the repeated running in a lowtemperature and high humidity environment. This point will be describedlater in detail.

Measurement Method

The plan view maximum area of the abrasive described above is acquiredby plane observation performed by using a scanning electron microscope.As the scanning electron microscope, a field emission (FE) type scanningelectron microscope (FE-SEM) is used. A scanning electron microscopeimage (SEM image) obtained by plane-observing and imaging the surface ofthe magnetic layer from the top by using the FE-SEM under the conditionsof an acceleration voltage of 5 kV, a working distance (W.D.) of 8 mm,and a magnification ratio of imaging of 20,000 times, is analyzed andaccordingly, the plan view maximum area of the abrasive is acquired. Thepercentage is calculated from the acquired plan view maximum area.Specific procedure is as follows.

1. Acquiring of SEM Image

An acceleration voltage is set as 5 kV, a working distance (W.D.) is setas 8 mm, and a magnification ratio of imaging is set as 20,000 times,and a SEM image is acquired as a secondary electron image, withoutperforming a sample coating before the imaging. As the scanning electronmicroscope (FE-SEM), FE-SEM 54800 manufactured by Hitachi, Ltd. can beused, for example. Values of Examples and Comparative Examples whichwill be described later are values obtained by using FE-SEM 54800manufactured by Hitachi, Ltd. as the FE-SEM and setting a probe currentas Normal.

2. Image Analysis

The image analysis of the SEM image acquired in the section 1. isperformed by the following procedure by using WinROOF manufactured byMitani Corporation as image analysis software. An area of each portiondescribed below is acquired as a value using a pixel as a unit.

(1) The image data (SEM (20K) jpg image) of the SEM image acquired inthe section 1. is dragged-and-dropped in WinROOF.

(2) A region having a size of 4.3 μm×6.3 μm of the image excluding apart where a magnification and a scale are displayed, is selected as ananalysis region.

(3) The image in the analysis region is subjected to binarizationprocessing. Specifically, 150 gradation is selected as a lower limitvalue, 255 gradation is selected as an upper limit value, and thebinarization processing is performed by setting the lower limit valueand the upper limit value as threshold values.

(4) By performing the binarization processing, an area of each whiteshining portion of the analysis region is acquired. Specifically, acommand of measurement→shape characteristics→area is executed in theimage analysis software WinROOF.

(5) The total area (4.3 μm×6.3 μm) of the analysis region is set as100%, a percentage of the area of each portion acquired in (4) withrespect to the total area is calculated, and a maximum value of thepercentage of the area of each portion is acquired.

(6) The procedure of (2) to (5) is executed four times by changing theposition of the analysis region (N=4).

(7) An arithmetical mean (that is, arithmetical mean of four maximumvalues) of the maximum values respectively acquired in (5) during theexecution of the procedure four times is calculated, and the calculatedvalue is set as the plan view maximum area of the abrasive. A percentageof the plan view maximum area acquired as described above occupying thetotal area of the analysis region is calculated and the calculatedpercentage is set as the plan view maximum area percentage of theabrasive.

Adjustment Method

By allowing the abrasive to be present in the magnetic layer in a finestate, it is possible to realize a state where the abrasive is presentin the magnetic layer in a state where the percentage is equal to orgreater than 0.02% and less than 0.06%. In order to allow the abrasiveto be present in the magnetic layer in a fine state, it is preferablethat an abrasive having a small particle size is used, the aggregate ofthe abrasive is prevented and the abrasive is dispersed in the magneticlayer without being unevenly distributed. As one method thereof, amethod of reinforcing the dispersion conditions of the abrasive at thetime of preparing a magnetic layer forming composition is used. Forexample, separate dispersing the abrasive and the ferromagnetic powderis one aspect of the reinforcement of the dispersion conditions. Theseparate dispersing is more specifically a method of preparing amagnetic layer forming composition through a step of mixing an abrasiveliquid including an abrasive and a solvent (here, substantially notincluding ferromagnetic powder) with a magnetic solution including theferromagnetic powder, a solvent, and a binding agent. By performing themixing after separately dispersing the abrasive and the ferromagneticpowder as described above, it is possible to increase dispersibility ofthe abrasive of the magnetic layer forming composition. The expressionof “substantially not including ferromagnetic powder” means that theferromagnetic powder is not added as a constituent component of theabrasive liquid, and a small amount of the ferromagnetic powder presentas impurities being mixed without intention is allowed. By arbitrarilycombining methods such as use of dispersion media having a small size(for example, decreasing a diameter of dispersion beads in beadsdispersion), a high degree of filling of dispersion media of adispersion device, and a dispersing process performed for a long time,other than the separate dispersing or in addition to the separatedispersing, it is possible to reinforce the dispersion conditions.

In addition, the use of a dispersing agent for improving dispersibilityof the abrasive can also be one aspect of the reinforcement of thedispersion conditions of the abrasive. Here, the dispersing agent forimproving dispersibility of the abrasive is a component which canincrease dispersibility of the abrasive in the magnetic layer formingcomposition and/or the abrasive liquid, compared to a state where thisagent is not present. As a compound which can function as such adispersing agent, an aromatic hydrocarbon compound including a phenolichydroxyl group can be used. The “phenolic hydroxyl group” is a hydroxylgroup directly combined with an aromatic ring. The aromatic ringincluded in the aromatic hydrocarbon compound may have a monocyclic orpolycyclic structure, or may a fused ring. From a viewpoint of improvingdispersibility of the abrasive, an aromatic hydrocarbon compoundincluding a benzene ring or a naphthalene ring is preferable. Inaddition, the aromatic hydrocarbon compound may include a substituentother than the phenolic hydroxyl group. Examples of the substituentother than the phenolic hydroxyl group include a halogen atom, an alkylgroup, an alkoxy group, an amino group, an acyl group, a nitro group, anitroso group, and a hydroxyalkyl group, and a halogen atom, an alkylgroup, an alkoxy group, an amino group, and a hydroxyalkyl group arepreferable. The phenolic hydroxyl group included in one molecule of thearomatic hydrocarbon compound may be 1, 2, 3, or more.

As one preferable aspect of the aromatic hydrocarbon compound includinga phenolic hydroxyl group, a compound represented by General Formula100.

[In General Formula 100, two of X¹⁰¹ to X¹⁰⁸ are hydroxyl groups andother six components each independently represent a hydrogen atom or asubstituent.]

In the compound represented by General Formula 100, a site ofsubstitution of the two hydroxyl groups (phenolic hydroxyl groups) isnot particularly limited.

In the compound represented by General Formula 100, two of X¹⁰¹ to X¹⁰⁸are hydroxyl groups (phenolic hydroxyl groups) and other six componentseach independently represent a hydrogen atom or a substituent. Inaddition, among X¹⁰¹ to X¹⁰⁸, all of portions other than the twohydroxyl groups may be hydrogen atoms or some or all of the portions maybe substituents. As the substituent, the substituents described abovecan be used. As the substituent other than the two hydroxyl groups, oneor more phenolic hydroxyl groups may be included. From a viewpoint ofimproving dispersibility of the abrasive, it is preferable that thecomponents other than the two hydroxyl groups among X¹⁰¹ to X¹⁰⁸ are notphenolic hydroxyl groups. That is, the compound represented by GeneralFormula 100 is preferably dihydroxynaphthalene or a derivative thereofand more preferably 2,3-dihydroxynaphthalene or a derivative thereof.Examples of a preferable substituent as the substituent represented byX¹⁰¹ to X¹⁰⁸ include a halogen atom (for example, a chlorine atom, abromine atom), an amino group, an alkyl group having 1 to 6 (preferably1 to 4) carbon atoms, a methoxy group and an ethoxy group, an acylgroup, a nitro group, a nitroso group, and a —CH₂OH group.

As the dispersing agent for improving dispersibility of the abrasive,descriptions disclosed in paragraphs 0024 to 0028 of JP2014-179149A canbe referred to.

The content of the dispersing agent for improving dispersibility of theabrasive described above can be used, for example, 0.5 to 20.0 parts bymass and is preferably 1.0 to 10.0 parts by mass with respect to 100.0parts by mass of the abrasive, at the time of preparing the magneticlayer forming composition, preferably at the time of preparing theabrasive liquid.

The “abrasive” means non-magnetic powder having Mohs hardness exceeding8 and is preferably non-magnetic powder having Mohs hardness equal to orgreater than 9. The abrasive may be powder of inorganic substances(inorganic powder) or may be powder of organic substances (organicpowder). The abrasive is more preferably inorganic powder having Mohshardness exceeding 8 and even more preferably inorganic powder havingMohs hardness equal to or greater than 9. A maximum value of Mohshardness is 10 of diamond. Specifically, powders of alumina (Al₂O₃),silicon carbide, boron carbide (B₄C), TiC, cerium oxide, zirconium oxide(ZrO₂), diamond, and the like can be used as the abrasive, and amongthese, alumina powder is preferable. The aromatic hydrocarbon compoundincluding a phenolic hydroxyl group described above is particularlypreferably used as a dispersing agent for improving dispersibility ofalumina powder. There are mainly two kinds of alumina having an alphatype crystal form and a gamma type crystal form. Both can be used, it ispreferable to use alumina (α-alumina) having an alpha type crystal form,from viewpoints of realizing higher hardness and contributing to theimprovement of abrasion properties and the improvement of the strengthof the magnetic layer. A gelatinization ratio of α-alumina is preferablyequal to or greater than 50% from a viewpoint of hardness. The shape ofthe particles of the abrasive may be any shape of an acicular shape, aspherical shape, and a dice shape.

In order to obtain a magnetic layer in which the abrasive is present ina fine state, it is preferable to use an abrasive having a smallparticle size as the abrasive. As an index of the particle size of theabrasive, a BET specific surface area can be used. A large BET specificsurface area means a small particle size. From a viewpoint of a smallparticle size, the BET specific surface area of the abrasive ispreferably equal to or greater than 14 m²/g, more preferably equal to orgreater than 15 m²/g, even more preferably equal to or greater than 18m²/g, and still more preferably equal to or greater than 20 m²/g. Inaddition, from a viewpoint of ease of improvement of dispersibility, anabrasive having a BET specific surface area equal to or smaller than 40m²/g is preferably used.

A preparing method of the magnetic layer forming composition includingthe abrasive will be described later in detail.

cos θ

In the magnetic tape, the tilt cos θ of the ferromagnetic hexagonalferrite powder with respect to the surface of the magnetic layeracquired by the cross section observation performed by using a scanningtransmission electron microscope is 0.85 to 1.00. The cos θ is morepreferably equal to or greater than 0.89, even more preferably equal toor greater than 0.90, still more preferably equal to or greater than0.92, and still even more preferably equal to or greater than 0.95.Meanwhile, in a case where all of the hexagonal ferrite particles havingan aspect ratio and a length in a long axis direction which will bedescribed later are present to be parallel to the surface of themagnetic layer, the cos θ becomes 1.00 which is the maximum value.According to the research of the inventor, it is found that, as thevalue of the cos θ increases, a deterioration of electromagneticconversion characteristics during the repeated running tends to beprevented. That is, in the magnetic tape having the total thickness ofthe non-magnetic layer and the magnetic layer equal to or smaller than0.60 μm, a great value of the cos θ is preferable, from a viewpoint ofpreventing a deterioration of electromagnetic conversion characteristicsduring the repeated running. Accordingly, in the magnetic tape, theupper limit of the cos θ is equal to or smaller than 1.00. The cos θ maybe, for example, equal to or smaller than 0.99. However, as describedabove, a great value of the cos θ is preferable, and thus, the cos θ mayexceed 0.99.

Measurement Method

The cos θ is acquired by the cross section observation performed byusing a scanning transmission electron microscope (STEM). The cos θ ofthe invention and the specification is a value acquired by the followingmethod.

(1) A cross section observation sample is manufactured by performing thecutting out from an arbitrarily determined position of the magnetic tapewhich is a target for acquiring the cos θ. The manufacturing of thecross section observation sample is performed by focused ion beam (FIB)processing using a gallium ion (Ga⁺) beam. A specific example of such amanufacturing method will be described later with Examples.

(2) The manufactured cross section observation sample is observed withthe STEM, and a STEM images are captured. The STEM images are capturedat positions of the same cross section observation sample arbitrarilyselected, except for selecting so that the imaging ranges are notoverlapped, and total 10 images are obtained. The STEM image is aSTEM-high-angle annular dark field (HAADF) image which is captured at anacceleration voltage of 300 kV and a magnification ratio of imaging of450,000, and the imaging is performed so that entire region of themagnetic layer in a thickness direction is included in one image. Theentire region of the magnetic layer in the thickness direction is aregion from the surface of the magnetic layer observed in the crosssection observation sample to an interface between the magnetic layerand the adjacent layer, and is normally a region therefrom to aninterface of the non-magnetic layer.

(3) In each STEM image obtained as described above, a linear lineconnecting both ends of a line segment showing the surface of themagnetic layer is determined as a reference line. In a case where theSTEM image is captured so that the magnetic layer side of the crosssection observation sample is positioned on the upper side of the imageand the non-magnetic support side is positioned on the lower side, forexample, the linear line connecting both ends of the line segmentdescribed above is a linear line connecting an intersection between aleft side of the image (normally, having a rectangular or square shape)of the STEM image and the line segment, and an intersection between aright side of the STEM image and the line segment to each other.

(4) Among the hexagonal ferrite particles observed in the STEM image, anangle θ formed by the reference line and the long axis direction of thehexagonal ferrite particles (primary particles) having an aspect ratioin a range of 1.5 to 6.0 and a length in the long axis direction equalto or greater than 10 nm is measured, and regarding the measured angleθ, the cos θ is calculated as a cos θ based on a unit circle. Thecalculation of the cos θ is performed with 30 particles arbitrarilyextracted from the hexagonal ferrite particles having the aspect ratioand the length in the long axis direction in each STEM image.

(5) The measurement and the calculation are respectively performed for10 images, the values of the acquired cos θ of the 30 hexagonal ferriteparticles of each image, that is, 300 hexagonal ferrite particles intotal of the 10 images, are averaged. The arithmetical mean acquired asdescribed above is set as the tilt cos θ of the ferromagnetic hexagonalferrite powder with respect to the surface of the magnetic layeracquired by the cross section observation performed by using thescanning transmission electron microscope.

Here, the “aspect ratio” observed in the STEM image is a ratio of“length in the long axis direction/length in a short axis direction” ofthe hexagonal ferrite particles.

The “long axis direction” means a direction when an end portion close tothe reference line and an end portion far from the reference line areconnected to each other, among the end portions which are most separatedfrom each other, in the image of one hexagonal ferrite particle observedin the STEM image. In a case where a line segment connecting one endportion and the other end portion is parallel with the reference line, adirection parallel to the reference line becomes the long axisdirection.

The “length in the long axis direction” means a length of a line segmentdrawn by connecting end portions which are most separated from eachother, in the image of one hexagonal ferrite particle observed in theSTEM image. Meanwhile, the “length in the short axis direction” means alength of the longest line segment, among the line segments connectingtwo intersections between an outer periphery of the image of theparticle and a perpendicular line with respect to the long axisdirection.

In addition, the angle θ formed by the reference line and the tilt ofthe particle in the long axis direction is determined to be in a rangeof 0° to 90°, by setting an angle of the long axis direction parallel tothe reference line as 0°. Hereinafter, the angle θ will be furtherdescribed with reference to the drawings.

FIG. 1 and FIG. 2 are explanatory diagrams of the angle θ. In FIG. 1 andFIG. 2, a reference numeral 101 indicates a line segment (length in thelong axis direction) drawn by connecting end portions which are mostseparated from each other, a reference numeral 102 indicates thereference line, and a reference numeral 103 indicates an extended lineof the line segment (reference numeral 101). In this case, as the angleformed by the reference line 102 and the extended line 103, θ1 and θ2are exemplified as shown in FIG. 1 and FIG. 2. Here, a smaller angle isused from the θ1 and θ2, and this is set as the angle θ. Accordingly, inthe aspect shown in FIG. 1, the θ1 is set as the angle θ, and in theaspect shown in FIG. 2, θ2 is set as the angle θ. A case where θ1=θ2 isa case where the angle θ=90°. The cos θ based on the unit circle becomes1.00, in a case where the θ=0°, and becomes 0, in a case where theθ=90°.

The magnetic tape includes the abrasive and the ferromagnetic hexagonalferrite powder in the magnetic layer, and cos θ is 0.85 to 1.00. Theinventor has thought that hexagonal ferrite particles satisfying theaspect ratio and the length in the long axis direction among thehexagonal ferrite particles configuring the ferromagnetic hexagonalferrite powder included in the magnetic layer can support the abrasive.The inventor has thought that this point contributes the exhibiting of afunction of removing head attached materials, even the abrasive ispresent in the magnetic layer of the magnetic tape in a fine state. Thispoint will be further described below.

From the studies of the inventor, it was clear that electromagneticconversion characteristics are deteriorated, in a case where themagnetic tape repeatedly runs in a drive in a low temperature and highhumidity environment, while allowing the surface of the magnetic layerof the magnetic tape having the total thickness of the non-magneticlayer and the magnetic layer equal to or smaller than 0.60 μm and thehead to slide on each other.

Meanwhile, the abrasive can impart a function of removing head attachedmaterial (abrasion properties) to the surface of the magnetic layer.When the surface of the magnetic layer exhibits abrasion properties, itis possible to remove the head attached material generated due to thechipping of a part of the surface of the magnetic layer caused by thesliding between the surface of the magnetic layer and the head andattached to the head. However, the inventor has surmised that, in a casewhere the surface of the magnetic layer does not sufficiently exhibitthe abrasion properties, the head and the surface of the magnetic layerslide on each other in a state where the attached material is attachedto the head, the head attached material causes spacing loss, and as aresult, electromagnetic conversion characteristics are deteriorated. Theinventor has thought that the deterioration of abrasion properties ofthe surface of the magnetic layer occurs due to the abrasive present inthe vicinity of the surface of the magnetic layer, which is pressed intothe magnetic layer at the time of sliding on the head.

With respect to this, the inventor has considered that the pressing ofthe abrasive present in the vicinity of the surface of the magneticlayer into the magnetic layer due to the sliding on the head can beprevented by supporting the abrasive by the hexagonal ferrite particlessatisfying the aspect ratio and the length in the long axis direction.Thus, the inventor has surmised that it is possible to prevent adeterioration of abrasion properties of the surface of the magneticlayer and it is possible to prevent occurrence of a deterioration ofelectromagnetic conversion characteristics due to the effect of attachedmaterial attached to the head.

A squareness ratio is known as an index of a presence state (orientationstate) of the ferromagnetic hexagonal ferrite powder of the magneticlayer. However, according to the studies of the inventor, an excellentcorrelation was not observed between the squareness ratio and a degreeof prevention of the deterioration of electromagnetic conversioncharacteristics. The squareness ratio is a value indicating a ratio ofresidual magnetization with respect to saturated magnetization, and ismeasured using all of the particles as targets, regardless of the shapesand size of the particles included in the ferromagnetic hexagonalferrite powder. With respect to this, the cos θ is a value measured byselecting the hexagonal ferrite particles having the aspect ratio andthe length in the long axis direction in the ranges described above. Theinventor has thought that, due to such a difference between the cos θand the squareness ratio, an excellent correlation between thesquareness ratio and a degree of prevention of the deterioration ofelectromagnetic conversion characteristics is not observed, but thedeterioration of electromagnetic conversion characteristics may beprevented by controlling the cos θ.

However, this is merely a surmise, and the invention is not limitedthereto.

Adjustment Method

The magnetic tape can be manufactured through a step of applying amagnetic layer forming composition onto the non-magnetic layer. As anadjustment method of the cos θ, a method of controlling a dispersionstate of the ferromagnetic hexagonal ferrite powder of the magneticlayer forming composition is used. Regarding this viewpoint, theinventor has thought that, as dispersibility of the ferromagnetichexagonal ferrite powder in the magnetic layer forming composition isincreased, the hexagonal ferrite particles having the aspect ratio andthe length in the long axis direction in the ranges described above inthe magnetic layer formed by using this magnetic layer formingcomposition are easily oriented in a state closer to parallel to thesurface of the magnetic layer. As means for increasing dispersibility,any one or both of the following methods (1) and (2) are used.

(1) Adjustment of Dispersion Conditions

(2) Use of Dispersing Agent for Improving Dispersibility ofFerromagnetic Hexagonal Ferrite Powder

In addition, as means for increasing dispersibility, a method ofseparately dispersing the ferromagnetic hexagonal ferrite powder and theabrasive is also used. The separate dispersing is as described above.The inventor has surmised that the separate dispersing contributes to anincrease in dispersibility of the abrasive and also contributes to anincrease in dispersibility of the ferromagnetic hexagonal ferritepowder. In addition, it is also preferable that any one or both of themethods (1) and (2) is combined with the separate dispersion describedabove. In this case, by controlling the dispersion state of theferromagnetic hexagonal ferrite powder of the magnetic solution, it ispossible to control the dispersion state of the ferromagnetic hexagonalferrite powder of the magnetic layer forming composition obtainedthrough the step of mixing the magnetic solution with the abrasiveliquid.

Hereinafter, specific aspects of the methods (1) and (2) will bedescribed.

(1) Adjustment of Dispersion Conditions

A dispersing process of the magnetic layer forming composition,preferably the magnetic solution can be performed by adjusting thedispersion conditions thereof by using a well-known dispersing method.The dispersion conditions of the dispersing process, for example,include the types of a dispersion device, the types of dispersion mediaused in the dispersion device, and a retention time in the dispersiondevice (hereinafter, also referred to as a “dispersion retention time”).

As the dispersion device, various well-known dispersion devices using ashear force such as a ball mill, a sand mill, or a homomixer. Adispersing process having two or more stages may be performed byconnecting two or more dispersion devices to each other, or differentdispersion devices may be used in combination. A circumferential speedof a tip of the dispersion device is preferably 5 to 20 msec and morepreferably 7 to 15 msec.

As the dispersion medium, ceramic beads or glass beads are used, andzirconia beads are preferable. Two or more types of beads may be used incombination. A particle diameter of the dispersion medium is, forexample, 0.03 to 1 mm and is preferably 0.05 to 0.5 mm. In a case ofperforming the dispersing process having two or more stages byconnecting the dispersion devices as described above, the dispersionmedium having different particle diameters may be used in each stage. Itis preferable that the dispersion medium having a smaller particlediameter is used, as the stages are passed. A filling percentage of thedispersion medium can be, for example, 30% to 80% and preferably 50% to80% based on the volume.

The dispersion retention time may be suitably set b considering thecircumferential speed of the tip of the dispersion device and thefilling percentage of the dispersion medium, and can be, for example, 15to 45 hours and preferably 20 to 40 hours. In a case of performing thedispersing process having two or more stages by connecting thedispersion devices as described above, the total dispersion retentiontime of each stage is preferably in the range described above. Byperforming the dispersing process described above, it is possible toincrease the dispersibility of the ferromagnetic hexagonal ferritepowder and to adjust the cos θ to be 0.85 to 1.00.

(2) Use of Dispersing Agent for Improving Dispersibility ofFerromagnetic Hexagonal Ferrite Powder

It is possible to increase the dispersibility of the ferromagnetichexagonal ferrite powder by using a dispersing agent for improvingdispersibility of the ferromagnetic hexagonal ferrite powder at the timeof preparing the magnetic layer forming composition, preferably at thetime of preparing the magnetic solution. Here, the dispersing agent forimproving dispersibility of the ferromagnetic hexagonal ferrite is acomponent which can increase the dispersibility of the ferromagnetichexagonal ferrite powder of the magnetic layer forming compositionand/or the magnetic solution, compared to a state where the agent is notpresent. It is also possible to control the dispersion state of theferromagnetic hexagonal ferrite powder by changing the type and theamount of the dispersing agent included in the magnetic layer formingcomposition and/or the magnetic solution. As the dispersing agent forimproving dispersibility of the ferromagnetic hexagonal ferrite, adispersing agent which prevents aggregation of the hexagonal ferriteparticles configuring the ferromagnetic hexagonal ferrite powder andimparts suitable plasticity to the magnetic layer is also preferablyused, from a viewpoint of increasing durability of the magnetic layer.

As an aspect of the dispersing agent preferable for improving thedispersibility of the ferromagnetic hexagonal ferrite powder, apolyester chain-containing compound can be used. The polyesterchain-containing compound is preferable from a viewpoint of impartingsuitable plasticity to the magnetic layer. Here, the polyester chain isshown as E in General Formula A which will be described later. Specificaspects thereof include a polyester chain contained in General Formula1, a polyester chain represented by Formula 2-A, and a polyester chainrepresented by Formula 2-B which will be described later. The inventorhas surmised that, by mixing the polyester chain-containing compoundwith the magnetic layer forming composition and/or the magnetic solutiontogether with the ferromagnetic hexagonal ferrite powder, it is possibleto prevent aggregation of particles, due to the polyester chaininterposed between the hexagonal ferrite particles. However, this ismerely the surmise, and the invention is not limited thereto. Aweight-average molecular weight of the polyester chain-containingcompound is preferably equal to or greater than 1,000, from a viewpointof improving the dispersibility of the ferromagnetic hexagonal ferritepowder. In addition, the weight-average molecular weight of thepolyester chain-containing compound is preferably equal to or smallerthan 80,000. The inventor has thought that the polyesterchain-containing compound having a weight-average molecular weight equalto or smaller than 80,000 can increase the durability of the magneticlayer by exhibiting an operation of a plasticizer. The weight-averagemolecular weight of the invention and the specification is a valueobtained by performing reference polystyrene conversion of a valuemeasured by gel permeation chromatography (GPC). Specific examples ofthe measurement conditions will be described later. In addition, thepreferred range of the weight-average molecular weight will be alsodescribed later.

As a preferred aspect of the polyester chain-containing compound, acompound having a partial structure represented by General Formula A isused. In the invention and the specification, unless otherwise noted, agroup disclosed may include a substituent or may be non-substituted. Ina case where a given group includes a substituent, examples of thesubstituent include an alkyl group (for example, alkyl group having 1 to6 carbon atoms), a hydroxyl group, an alkoxy group (for example, alkoxygroup having 1 to 6 carbon atoms), a halogen atom (for example, afluorine atom, a chlorine atom, or a bromine atom), a cyano group, anamino group, a nitro group, an acyl group, carboxyl (salt) group. Inaddition, the “number of carbon atoms” of the group including asubstituent means the number of carbon atoms of a portion not includinga substituent.

In General Formula A, Q represents —O—, —CO—, —S—, —NR^(a)—, or a singlebond, T and R^(a) each independently represent a hydrogen atom or amonovalent substituent, E represents —(O-L^(A)-CO)a- or —(CO-L^(A)-O)a-,L^(A) represents a divalent linking group, a represents an integer equalto or greater than 2, b represents an integer equal to or greater than1, and * represents a bonding site with another partial structureconfiguring the polyester chain-containing compound.

In General Formula A, the number of L^(A) included is a value of a×b. Inaddition, the numbers of T and Q included are respectively the value ofb. In a case where a plurality of L^(A) are included in General FormulaA, the plurality of L^(A) may be the same as each other or differentfrom each other. The same applies to T and Q.

It is considered that the compound described above can preventaggregation of hexagonal ferrite particles due to a steric hindrancecaused by the partial structure, in the magnetic solution and themagnetic layer forming composition.

As a preferred aspect of the polyester chain-containing compound, acompound including a group which can be adsorbed to the surface of thehexagonal ferrite particles or the partial structure (hereinafter,referred to as an “adsorption part”) together with the polyester chainin a molecule is used. It is preferable that the polyester chain isincluded in the partial structure represented by General Formula A. Inaddition, it is more preferable that the partial structure and theadsorption part represented by General Formula A form a bond through *in General Formula A.

In one aspect, the adsorption part can be a functional group (polargroup) having polarity to be an adsorption point to the surface of thehexagonal ferrite particles. As a specific example, at least one polargroup selected from a carboxyl group (—COOH) and a salt thereof(—COO⁻M⁺), a sulfonic acid group (—SO₃H) and a salt thereof (—SO₃ ⁻M⁺),a sulfuric acid group (—OSO₃H) and a salt thereof (—OSO₃ ⁻M⁺), aphosphoric acid group (—P═O(OH)₂) and a salt thereof (—P═O(O⁻M⁺)₂), anamino group (—NR₂), —N⁺R₃, an epoxy group, a thiol group (—SH), and acyano group (—CN) (here, M⁺ represents a cation such as an alkali metalion and R represents a hydrogen atom or a hydrocarbon group) can beused. In addition, the “carboxyl (salt) group” means one or both of acarboxyl group and a salt thereof (carboxylic salt). The carboxylic saltis a state of a salt of the carboxyl group (—COOH) as described above.

As one aspect of the adsorption part, a polyalkyleneimine chain can alsobe used.

The types of the bond formed by the partial structure and the adsorptionpart represented by General Formula A are not particularly limited. Sucha bond is preferably selected from the group consisting of a covalentbond, a coordinate bond, and an ion bond, and a bond of different typesmay be included in the same molecule. It is considered that byefficiently performing the adsorption with respect to the hexagonalferrite particles through the adsorption part, it is possible to furtherincrease an aggregation prevention effect of the hexagonal ferriteparticles based on the steric hindrance caused by the partial structurerepresented by General Formula A.

In one aspect, the polyester chain-containing compound can include atleast one polyalkyleneimine chain. The polyester chain-containingcompound can preferably include a polyester chain in the partialstructure represented by General Formula A. As a preferred example ofthe polyester chain-containing compound, a polyalkyleneimine derivativeincluding a polyester chain selected from the group consisting of apolyester chain represented by Formula 2-A and a polyester chainrepresented by Formula 2-B as General Formula A is used. These exampleswill be described later in detail.

L¹ in Formula 2-A and L² in Formula 2-B each independently represent adivalent linking group, b11 in Formula 2-A and b21 in Formula 2-B eachindependently represent an integer equal to or greater than 2, b12 inFormula 2-A and b22 in Formula 2-B each independently represent 0 or 1,and X¹ in Formula 2-A and X² in Formula 2-B each independently representa hydrogen atom or a monovalent substituent.

In General Formula A, Q represents —O—, —CO—, —S—, —NR^(a)—, or a singlebond, and is preferably a portion represented by X in General Formula 1which will be described later, (—CO—)b12 in Formula 2-A or (—CO—)b22 inFormula 2-B.

In General Formula A, T and R^(a) each independently represent ahydrogen atom or a monovalent substituent and is preferably a portionrepresented by R in General Formula 1 which will be described later, X¹in Formula 2-A or X² in Formula 2-B.

In General Formula A, E represents —(O-L^(A)-CO)a- or —(CO-L^(A)-O)a-,L^(A) represents a divalent linking group, and a represents an integerequal to or greater than 2.

As a divalent linking group represented by L^(A), L in General Formula 1which will be described later, L¹ in Formula 2-A or L² in Formula 2-B ispreferably used.

In one aspect, the polyester chain-containing compound can include atleast one group selected from the group consisting of a carboxyl groupand a carboxylic salt. Such a polyester chain-containing compound canpreferably include a polyester chain in the partial structurerepresented by General Formula A. As a preferred example of thepolyester chain-containing compound, a compound represented by GeneralFormula 1 is used.

Compound Represented by General Formula 1

General Formula 1 is as described below.

(In General Formula 1, X represents —O—, —S—, or —NR¹—, R and R¹ eachindependently represent a hydrogen atom or a monovalent substituent, Lrepresents a divalent linking group, Z represents a n-valent partialstructure including at least one group (carboxyl (salt) group) selectedfrom the group consisting of a carboxyl group and a carboxylic salt, mrepresents an integer equal to or greater than 2, and n represents aninteger equal to or greater than 1.)

In General Formula 1, the number of L included is a value of m×n. Inaddition, the numbers of R and X included are respectively the value ofn. In a case where a plurality of L are included in General Formula 1,the plurality of L may be the same as each other or different from eachother. The same applies to R and X.

The compound represented by General Formula 1 has a structure (polyesterchain) represented by —((C═O)-L-O)m-, and a carboxyl (salt) group isincluded in the Z part as the adsorption part. It is considered that,when the compound represented by General Formula 1 is effectivelyadsorbed to the hexagonal ferrite particles by setting the carboxyl(salt) group included in the Z part as the adsorption part to thesurface of the hexagonal ferrite particles, it is possible to preventaggregation of the hexagonal ferrite particles caused by sterichindrance caused by the polyester chain.

In General Formula 1, X represents —O—, —S—, or —NR¹—, and R¹ representsa hydrogen atom or a monovalent substituent. As the monovalentsubstituent represented by R¹, an alkyl group, a hydroxyl group, analkoxy group, a halogen atom, a cyano group, an amino group, a nitrogroup, an acyl group, and a carboxyl (salt) group which is thesubstituent described above can be used, an alkyl group is preferablyused, an alkyl group having 1 to 6 carbon atoms is more preferably used,and a methyl group or an ethyl group is even more preferably used. R¹ isstill more preferably a hydrogen atom. X preferably represents —O—.

R represents a hydrogen atom or a monovalent substituent. R preferablyrepresents a monovalent substituent. As the monovalent substituentrepresented by R, a monovalent group such as an alkyl group, an arylgroup, a heteroaryl group, an alicyclic group, or a nonaromaticheterocyclic group, and a structure in which a divalent linking group isbonded to the monovalent group (that is, R has a structure in which adivalent linking group is bonded to the monovalent group and is amonovalent substituent bonding with X through the divalent linkinggroup) can be used, for example. As the divalent linking group, adivalent linking group configured of a combination of one or two or moreselected from the group consisting of —C(═O)—O—, —O—, —C(═O)—NR¹⁰—(R¹⁰represents a hydrogen atom or an alkyl group having 1 to 4 carbonatoms), —O—C(═O)—NH—, a phenylene group, an alkylene group having 1 to30 carbon atoms, and an alkenylene group having 2 to 30 carbon atoms canbe used, for example. As a specific example of the monovalentsubstituent represented by R, the following structures are used, forexample. In the following structures, * represent a bonding site with X.However, R is not limited to the following specific example.

In General Formula 1, L represents a divalent linking group. As thedivalent linking group, a divalent linking group which is configured ofa combination of one or two or more selected from the group consistingof an alkylene group which may have a linear, branched, or ringstructure, an alkenylene group which may have a linear, branched, orring structure, —C(═O)—, —O—, and an arylene group, and which mayinclude a substituent in the divalent linking group or a halogen atom asan anion can be used. More specifically, a divalent linking groupconfigured of a combination of one or two or more selected from analkylene group having 1 to 12 carbon atoms which may have a linear,branched, or ring structure, an alkenylene group having 1 to 6 carbonatoms which may have a linear, branched, or ring structure, —C(═O)—,—O—, and a phenylene group can be used. The divalent linking group ispreferably a divalent linking group having 1 to 10 carbon atoms, 0 to 10oxygen atoms, 0 to 10 halogen atoms, and 1 to 30 hydrogen atoms. As aspecific example, an alkylene group and the following structure areused. In the following structure, * represents a bonding site with theother structure in General Formula 1. However, the divalent linkinggroup is not limited to the following specific example.

L is preferably an alkylene group, more preferably an alkylene grouphaving 1 to 12 carbon atoms, even more preferably an alkylene grouphaving 1 to 5 carbon atoms, and still more preferably a non-substitutedalkylene group having 1 to 5 carbon atoms.

Z represents an n-valent partial structure including at least one group(carboxyl (salt) group) selected from the group consisting of a carboxylgroup and a carboxylic salt.

The number of the carboxyl (salt) group included in Z is at least 1,preferably equal to or greater than 2, and more preferably 2 to 4, forone Z.

Z can have a structure of one or more selected from the group consistingof a linear structure, a branched structure, and a cyclic structure.From a viewpoint of easiness of synthesis, Z is preferably a reactiveresidue of a carboxylic acid anhydride. For example, as a specificexample, the following structures are used. In the followingstructures, * represents a bonding site with the other structure inGeneral Formula 1. However, Z is not limited to the following specificexample.

The carboxylic acid anhydride is a compound having a partial structurerepresented by —(C═O)—O—(C═O)—. In the carboxylic acid anhydride, thepartial structure becomes a reactive site, and an oxygen atom and Z of—((C═O)-L-O)m- in General Formula 1 are bonded to each other through acarbonyl bond (—(C═O)—), and a carboxyl (salt) group is obtained. Thepartial structure generated as described above is a reactive residue ofa carboxylic acid anhydride. By synthesizing the compound represented byGeneral Formula 1 by using a compound having one partial structure—(C═O)—O—(C═O)—, as the carboxylic acid anhydride, it is possible toobtain a compound represented by General Formula 1 including amonovalent reactive residue of the carboxylic acid anhydride, and it ispossible to obtain a compound represented by General Formula 1 includinga divalent reactive residue of the carboxylic acid anhydride, by usingthe compound having two partial structures described above. The sameapplies to the compound represented by General Formula 1 including atri- or higher valent reactive residue of the carboxylic acid anhydride.As described above, n is an integer equal to or greater than 1, is, forexample, an integer of 1 to 4, and is preferably an integer of 2 to 4.

It is possible to obtain a compound represented by General Formula 1 ina case of n=2, by using the tetracarboxylic acid anhydride, for example,as the carboxylic acid anhydride. The tetracarboxylic acid anhydride isa carboxylic acid anhydride having two partial structures describedabove in one molecule, by dehydration synthesis of two carboxyl groups,in the compound including four carboxyl groups in one molecule. InGeneral Formula 1, the compound in which Z represents a reactive residueof the tetracarboxylic acid anhydride is preferable, from viewpoints offurther improving dispersibility of ferromagnetic hexagonal ferritepowder and durability of the magnetic layer. Examples of thetetracarboxylic acid anhydride include various tetracarboxylic acidanhydrides such as aliphatic tetracarboxylic acid anhydride, aromatictetracarboxylic acid anhydride, and polycyclic tetracarboxylic acidanhydride.

As the aliphatic tetracarboxylic acid anhydride, for example, variousaliphatic tetracarboxylic acid anhydrides disclosed in a paragraph 0040of JP2016-071926A can be used. As the aromatic tetracarboxylic acidanhydride, for example, various aromatic tetracarboxylic acid anhydridesdisclosed in a paragraph 0041 of JP2016-071926A can be used. As thepolycyclic tetracarboxylic acid anhydride, various polycyclictetracarboxylic acid anhydrides disclosed in a paragraph 0042 ofJP2016-071926A can be used.

In General Formula 1, m represents an integer equal to or greater than2. As described above, it is thought that the structure (polyesterchain) represented by —((C═O)-L-O)m- of the compound represented byGeneral Formula 1 contributes to the improvement of dispersibility andthe durability. From these viewpoints, m is preferably an integer of 5to 200, more preferably an integer of 5 to 100, and even more preferablyan integer of 5 to 60.

Weight-Average Molecular Weight

The weight-average molecular weight of the compound represented byGeneral Formula 1 is preferably 1,000 to 80,000 as described above andmore preferably 1,000 to 20,000. The weight-average molecular weight ofthe compound represented by General Formula 1 is even more preferablysmaller than 20,000, further more preferably equal to or smaller than12,000, and sill more preferably equal to or smaller than 10,000. Inaddition, the weight-average molecular weight of the compoundrepresented by General Formula 1 is preferably equal to or greater than1,500 and more preferably equal to or greater than 2,000. Regarding thecompound represented by General Formula 1, the weight-average molecularweight shown in Examples which will be described later is a valueobtained by performing reference polystyrene conversion of a valuemeasured by GPC under the following measurement conditions. In addition,the weight-average molecular weight of a mixture of two or more kinds ofstructural isomers is a weight-average molecular weight of two or morekinds of structural isomers included in this mixture.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard column: TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M(manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm,three types of columns are connected in series)

Eluent: Tetrahydrofuran (THF), containing a stabilizer(2,6-di-t-butyl-4-methylphenol)

Flow rate of eluent: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3 mass %

Sample introduction amount: 10 μL

Synthesis Method

The compound represented by General Formula 1 described above can besynthesized by a well-known method. As an example of the synthesismethod, a method of allowing a reaction such as a ring-opening additionreaction between the carboxylic acid anhydride and a compoundrepresented by General Formula 2 can be used, for example. In GeneralFormula 2, R, X, L, and m are the same as those in General Formula 1. Arepresents a hydrogen atom, an alkali metal atom, or quaternary ammoniumbase and is preferably a hydrogen atom.

In a case of using a butanetetracarboxylic acid anhydride, for example,the reaction between the carboxylic acid anhydride and a compoundrepresented by General Formula 2 is performed by mixing thebutanetetracarboxylic acid anhydride at a percentage of 0.4 to 0.5 moleswith respect to 1 equivalent of a hydroxyl group, and heating andstirring the mixture approximately for 3 to 12 hours, under the absenceof solvent, if necessary, under the presence of an organic solventhaving a boiling point equal to or higher than 50° C., further, areaction catalyst such as tertiary amine or inorganic base. Even in acase of using other carboxylic acid anhydride, a reaction between thecarboxylic acid anhydride and the compound represented by GeneralFormula 2 can be performed under the reaction conditions described aboveor under well-known reaction conditions.

After the reaction, post-step such as purification may be performed, ifnecessary.

In addition, the compound represented by General Formula 2 can also beobtained by using a commercially available product or by a well-knownpolyester synthesis method. For example, as the polyester synthesismethod, ring-opening polymerization of lactone can be used. As thering-opening polymerization of lactone, descriptions disclosed inparagraphs 0050 and 0051 of JP2016-071926A can be referred to. However,the compound represented by General Formula 2 is not limited to acompound obtained by the ring-opening polymerization of lactone, and canalso be a compound obtained by a well-known polyester synthesis method,for example, polycondensation of polyvalent carboxylic acid andpolyhydric alcohol or polycondensation of hydroxycarboxylic acid.

The synthesis method described above is merely an example and there isno limitation regarding the synthesis method of the compound representedby General Formula 1. Any well-known synthesis method can be usedwithout limitation, as long as it is a method capable of synthesizingthe compound represented by General Formula 1. The reaction productafter the synthesis can be used for forming the magnetic layer, as itis, or by purifying the reaction product by a well-known method, ifnecessary. The compound represented by General Formula 1 may be usedalone or in combination of two or more kinds having differentstructures, in order to form the magnetic layer. In addition, thecompound represented by General Formula 1 may be used as a mixture oftwo or more kinds of structural isomers. For example, in a case ofobtaining two or more kinds of structural isomers by the synthesisreaction of the compound represented by General Formula 1, the mixturecan also be used for forming the magnetic layer.

As the compound represented by General Formula 1, various compoundsincluded in reaction products shown in synthesis examples in Examplesdisclosed in JP2016-071926 can be used. For example, as a specificexample thereof, compounds shown in Table 1 can be used. Aweight-average molecular weight shown in Table 1 is a weight-averagemolecular weight of the compound represented by structural formula shownin Table 1 or a weight-average molecular weight of the compoundrepresented by structural formula shown in Table 1 and a mixture ofstructural isomers thereof.

TABLE 1 Weight- average molecular Types Structural Formula weightCompound 1

9200 Compound 2

6300 Compound 3

5300 Compound 4

8000 Compound 5

8700 Compound 6

8600 Compound 7

6200 Compound 8

8000

As an aspect of a preferred example of the compound having the partialstructure and the adsorption part represented by General Formula A, apolyalkyleneimine derivative including a polyester chain represented byFormula 2-A or 2-B as General Formula A is used. Hereinafter, thepolyalkyleneimine derivative will be described.

Polyalkyleneimine Derivative

The polyalkyleneimine derivative is a compound including at least onepolyester chain selected from the group consisting of a polyester chainrepresented by Formula 2-A and a polyester chain represented by Formula2-B, and a polyalkyleneimine chain having a number average molecularweight of 300 to 3,000. A percentage of the polyalkyleneimine chainoccupying the compound is preferably smaller than 5.0 mass %.

The polyalkyleneimine derivative includes a polyalkyleneimine chainwhich is an aspect of the adsorption part described above. In addition,it is thought that the steric hindrance caused by the polyester chainincluded in the polyalkyleneimine derivative is caused in the magneticlayer forming composition and/or the magnetic solution, and accordingly,it is possible to prevent aggregation of the hexagonal ferriteparticles.

Hereinafter, the polyester chain and the polyalkyleneimine chainincluded in the polyalkyleneimine derivative will be described.

Polyester Chain

Structure of Polyester Chain

The polyalkyleneimine derivative includes at least one polyester chainselected from the group consisting of a polyester chain represented byFormula 2-A and a polyester chain represented by Formula 2-B, togetherwith a polyalkyleneimine chain which will be described later. In oneaspect, the polyester chain is bonded to an alkyleneimine chainrepresented by Formula A which will be described later by a nitrogenatom N included in Formula A and a carbonyl bond —(C═O)— at *¹ ofFormula A, and —N—(═O)— can be formed. In addition, in another aspect,an alkyleneimine chain represented by Formula B which will be describedlater and the polyester chain can form a salt crosslinking group by anitrogen cation N⁺ in Formula B and an anionic group including apolyester chain. As the salt crosslinking group, a component formed byan oxygen anion O⁻ included in the polyester chain and N⁺ in Formula Bcan be used.

As the polyester chain bonded to the alkyleneimine chain represented byFormula A by a nitrogen atom N included in Formula A and a carbonyl bond—(C═O)—, the polyester chain represented by Formula 2-A can be used. Thepolyester chain represented by Formula 2-A can be bonded to thealkyleneimine chain represented by Formula A by forming —N—(═O)— by anitrogen atom included in the alkyleneimine chain and a carbonyl group—(C═O)— included in the polyester chain at the bonding site representedby *¹.

In addition, as the polyester chain bonded to the alkyleneimine chainrepresented by Formula B by forming a salt crosslinking group by N⁺ inFormula B and an anionic group including the polyester chain, thepolyester chain represented by Formula 2-B can be used. The polyesterchain represented by Formula 2-B can form N⁺ in Formula B and a saltcrosslinking group by an oxygen anion O⁻.

L¹ in Formula 2-A and L² in Formula 2-B each independently represent adivalent linking group. As the divalent linking group, an alkylene grouphaving 3 to 30 carbon atoms can be preferably used. In a case where thealkylene group includes a substituent, the number of carbon atoms of thealkylene group is the number of carbon atoms of a part (main chain part)excluding the substituent, as described above.

b11 in Formula 2-A and b21 Formula 2-B each independently represent aninteger equal to or greater than 2, for example, an integer equal to orsmaller than 200. The number of lactone repeating units shown in Table 3which will be described later corresponds to b11 in Formula 2-A or b21Formula 2-B.

b12 in Formula 2-A and b22 Formula 2-B each independently represent 0 or1.

X¹ in Formula 2-A and X² Formula 2-B each independently represent ahydrogen atom or a monovalent substituent. As the monovalentsubstituent, a monovalent substituent selected from the group consistingof an alkyl group, a haloalkyl group (for example, fluoroalkyl group),an alkoxy group, a polyalkyleneoxyalkyl group, and an aryl group can beused.

The alkyl group may include a substituent or may be non-substituted. Asthe alkyl group including a substituent, an alkyl group (hydroxyalkylgroup) substituted with a hydroxyl group, and an alkyl group substitutedwith one or more halogen atoms are preferable. In addition, an alkylgroup (haloalkyl group) in which all of hydrogen atoms bonded to carbonatoms are substituted with halogen atoms is also preferable. As thehalogen atom, a fluorine atom, a chlorine atom, or a bromine atom can beused. The alkyl group is more preferably an alkyl group having 1 to 30carbon atoms, and even more preferably an alkyl group having 1 to 10carbon atoms. The alkyl group may have any of a linear, branched, andcyclic structure. The same applies to the haloalkyl group.

Specific examples of substituted or non-substituted alkyl group orhaloalkyl group include a methyl group, an ethyl group, a propyl group,a butyl group, a pentyl group, a hexyl group, a heptyl group, an octylgroup, a nonyl group, a decyl group, a undecyl group, a dodecyl group, atridecyl group, a pentadecyl group, a hexadecyl group, a heptadecylgroup, an octadecyl group, an eicosyl group, an isopropyl group, anisobutyl group, an isopentyl group, a 2-ethylhexyl group, a tert-octylgroup, a 2-hexyldecyl group, a cyclohexyl group, a cyclopentyl group, acyclohexylmethyl group, an octylcyclohexyl group, a 2-norbornyl group, a2,2,4-trimethylpentyl group, an acetylmethyl group, an acetylethylgroup, a hydroxymethyl group, a hydroxyethyl group, a hydroxypropylgroup, a hydroxybutyl group, a hydroxypentyl group, a hydroxyhexylgroup, a hydroxyheptyl group, a hydroxyoctyl group, a hydroxynonylgroup, a hydroxydecyl group, a chloromethyl group, a dichloromethylgroup, a trichloromethyl group, a bromomethyl group, a1,1,1,3,3,3-hexafluoroisopropyl group, a heptafluoropropyl group, apentadecafluoroheptyl group, a nonadecafluorononyl group, ahydroxyundecyl group, a hydroxydodecyl group, a hydroxypentadecyl group,a hydroxyheptadecyl group, and a hydroxyoctadecyl group.

Examples of the alkoxy group include a methoxy group, an ethoxy group, apropyloxy group, a hexyloxy group, a methoxyethoxy group, amethoxyethoxyethoxy group, and a methoxyethoxyethoxymethyl group.

The polyalkyleneoxyalkyl group is a monovalent substituent representedby R¹⁰(OR¹¹)n1(O)m1-. R¹⁰ represents an alkyl group, R¹¹ represents analkylene group, n1 represents an integer equal to or greater than 2, andml represents 0 or 1.

The alkyl group represented by R¹⁰ is as described regarding the alkylgroup represented by X¹ or X². For the specific description of thealkylene group represented by R¹¹, the description regarding the alkylgroup represented by X¹ or X² can be applied by replacing the alkylgroup with an alkylene group obtained by removing one hydrogen atom fromthe alkylene group (for example, by replacing the methyl group with amethylene group). n1 is an integer equal to or greater than 2, forexample, an integer equal to or smaller than 10, and preferably equal toor smaller than 5.

The aryl group may include a substituent or may be annelated, and morepreferably an aryl group having 6 to 24 carbon atoms, and examplesthereof include a phenyl group, a 4-methylphenyl group, 4-phenylbenzoicacid, a 3-cyanophenyl group, a 2-chlorophenyl group, and a 2-naphthylgroup.

The polyester chain represented by Formula 2-A and the polyester chainrepresented by Formula 2-B can have a polyester-derived structureobtained by a well-known polyester synthesis method. As the polyestersynthesis method, ring-opening polymerization of lactone disclosed inparagraphs 0056 and 0057 of JP2015-28830A can be used. However, thestructure of the polyester chain is not limited to the polyester-derivedstructure obtained by the ring-opening polymerization of lactone, andcan be a polyester-derived structure obtained by a well-known polyestersynthesis method, for example, polycondensation of polyvalent carboxylicacid and polyhydric alcohol or polycondensation of hydroxycarboxylicacid.

Number Average Molecular Weight of Polyester Chain

A number average molecular weight of the polyester chain is preferablyequal to or greater than 200, more preferably equal to or greater than400, and even more preferably equal to or greater than 500, from aviewpoint of improvement of dispersibility of ferromagnetic hexagonalferrite powder. In addition, from the same viewpoint, the number averagemolecular weight of the polyester chain is preferably equal to orsmaller than 100,000 and more preferably equal to or smaller than50,000. As described above, it is considered that the polyester chainfunctions to cause steric hindrance in the magnetic layer formingcomposition and/or the magnetic solution and preventing the aggregationof the hexagonal ferrite particles. It is assumed that the polyesterchain having the number average molecular weight described above canexhibit such an operation in an excellent manner. The number averagemolecular weight of the polyester chain is a value obtained byperforming reference polystyrene conversion of a value measured by GPC,regarding polyester obtained by hydrolysis of a polyalkyleneiminederivative. The value acquired as described above is the same as a valueobtained by performing reference polystyrene conversion of a valuemeasured by GPC regarding polyester used for synthesis of thepolyalkyleneimine derivative. Accordingly, the number average molecularweight acquired regarding polyester used for synthesis of thepolyalkyleneimine derivative can be used as the number average molecularweight of the polyester chain included in the polyalkyleneiminederivative. For the measurement conditions of the number averagemolecular weight of the polyester chain, the measurement conditions ofthe number average molecular weight of polyester in a specific examplewhich will be described later can be referred to.

Polyalkyleneimine Chain

Number Average Molecular Weight

The number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative is a value obtained byperforming reference polystyrene conversion of a value measured by GPC,regarding polyalkyleneimine obtained by hydrolysis of apolyalkyleneimine derivative. The value acquired as described above isthe same as a value obtained by performing reference polystyreneconversion of a value measured by GPC regarding polyalkyleneimine usedfor synthesis of the polyalkyleneimine derivative. Accordingly, thenumber average molecular weight acquired regarding polyalkyleneimineused for synthesis of the polyalkyleneimine derivative can be used asthe number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative. For the measurementconditions of the number average molecular weight of thepolyalkyleneimine chain, a specific example which will be describedlater can be referred to. In addition, the polyalkyleneimine is apolymer which can be obtained by ring-opening polymerization ofalkyleneimine. In the polyalkyleneimine derivative, the term “polymer”is used to include a homopolymer including a repeating unit in the samestructure and a copolymer including a repeating unit in two or morekinds of different structures.

The hydrolysis of the polyalkyleneimine derivative can be performed byvarious methods which are normally used as a hydrolysis method of ester.For details of such a method, description of a hydrolysis methoddisclosed in “The Fifth Series of Experimental Chemistry Vol. 14Synthesis of Organic Compounds II—Alcohol.Amine” (Chemical Society ofJapan, Maruzen Publication, issued August, 2005) pp. 95 to 98, anddescription of a hydrolysis method disclosed in “The Fifth Series ofExperimental Chemistry Vol. 16 Synthesis of Organic CompoundsIV-Carboxylic acid—Amino Acid—Peptide” (Chemical Society of Japan,Maruzen Publication, issued March, 2005) pp. 10 to 15 cam be referredto, for example.

The polyalkyleneimine is decomposed from the obtained hydrolyzate bywell-known separating means such as liquid chromatography, and thenumber average molecular weight thereof can be acquired.

The number average molecular weight of the polyalkyleneimine chainincluded in the polyalkyleneimine derivative is in a range of 300 to3,000. The inventors have surmised that when the number averagemolecular weight of the polyalkyleneimine chain is in the rangedescribed above, the polyalkyleneimine derivative can be effectivelyadsorbed to the surface of the hexagonal ferrite particles. The numberaverage molecular weight of the polyalkyleneimine chain is preferablyequal to or greater than 500, from a viewpoint of adsorption propertiesto the surface of the hexagonal ferrite particles. From the sameviewpoint, the number average molecular weight is preferably equal to orsmaller than 2,000.

Percentage of Polyalkyleneimine Chain Occupying PolyalkyleneimineDerivative

As described above, the inventors have considered that thepolyalkyleneimine chain included in the polyalkyleneimine derivative canfunction as an adsorption part to the surface of the hexagonal ferriteparticles. A percentage of the polyalkyleneimine chain occupying thepolyalkyleneimine derivative (hereinafter, also referred to as a“polyalkyleneimine chain percentage”) is preferably smaller than 5.0mass %, from a viewpoint of increasing the dispersibility of theferromagnetic hexagonal ferrite powder. From a viewpoint of improvingthe dispersibility of the ferromagnetic hexagonal ferrite powder, thepolyalkyleneimine chain percentage is more preferably equal to orsmaller than 4.9 mass %, even more preferably equal to or smaller than4.8 mass %, further more preferably equal to or smaller than 4.5 mass %,still more preferably equal to or smaller than 4.0 mass %, and stilleven more preferably equal to or smaller than 3.0 mass %. In addition,from a viewpoint of improving the dispersibility of the ferromagnetichexagonal ferrite powder, the polyalkyleneimine chain percentage ispreferably equal to or greater than 0.2 mass %, more preferably equal toor greater than 0.3 mass %, and even more preferably equal to or greaterthan 0.5 mass %.

The percentage of the polyalkyleneimine chain described above can becontrolled, for example, according to a mixing ratio ofpolyalkyleneimine and polyester used at the time of synthesis.

The percentage of the polyalkyleneimine chain occupying thepolyalkyleneimine derivative can be calculated from an analysis resultobtained by element analysis such as nuclear magnetic resonance (NMR),more specifically, ¹H-NMR and ¹³C-NMR, and a well-known method. Thevalue calculated as described is the same as a theoretical valueacquired from a compounding ratio of a synthesis raw material in thepolyalkyleneimine derivative, and thus, the theoretical value acquiredfrom the compounding ratio can be used as the percentage of thepolyalkyleneimine chain occupying the polyalkyleneimine derivative.

Structure of Polyalkyleneimine Chain

The polyalkyleneimine chain has a polymer structure including the sameor two or more different alkyleneimine chains. As the alkyleneiminechain included, an alkyleneimine chain represented by Formula A and analkyleneimine chain represented by Formula B can be used. In thealkyleneimine chains represented by the following formulae, thealkyleneimine chain represented by Formula A can include a bonding sitewith a polyester chain. In addition, the alkyleneimine chain representedby Formula B can be bonded to a polyester chain by the salt crosslinkinggroup described above. The polyalkyleneimine derivative can have astructure in which one or more polyester chains are bonded to thepolyalkyleneimine chain, by including one or more alkyleneimine chains.In addition, the polyalkyleneimine chain may be formed of only a linearstructure or may have a branched tertiary amine structure. It ispreferable that the polyalkyleneimine chain has a branched structure,from a viewpoint of further improving the dispersibility. As a componenthaving a branched structure, a component bonded to an adjacentalkyleneimine chain at *¹ in Formula A and a component bonded to anadjacent alkyleneimine chain at *² in Formula B can be used.

In Formula A, R¹ and R² each independently represent a hydrogen atom oran alkyl group, a1 represents an integer equal to or greater than 2, and*¹ represents a bonding site with a polyester chain, an adjacentalkyleneimine chain, a hydrogen atom, or a substituent.

In Formula B, R³ and R⁴ each independently represent a hydrogen atom oran alkyl group, and a2 represents an integer equal to or greater than 2.The alkyleneimine chain represented by Formula B is bonded to apolyester chain including an anionic group by forming a saltcrosslinking group by N⁺ in Formula B and an anionic group included inthe polyester chain.

* in Formula A and Formula B and *² in Formula B each independentlyrepresent a site to be bonded to an adjacent alkyleneimine chain, ahydrogen atom, or a sub stituent.

Hereinafter, Formula A and Formula B will be further described indetail.

R¹ and R² in Formula A and R³ and R⁴ in Formula B each independentlyrepresent a hydrogen atom or an alkyl group. As the alkyl group, forexample, an alkyl group having 1 to 6 carbon atoms can be used, and thealkyl group is preferably an alkyl group having 1 to 3 carbon atoms,more preferably a methyl group or an ethyl group, and even morepreferably a methyl group. As an aspect of a combination of R¹ and R² inFormula A, an aspect in which one is a hydrogen atom and the other is analkyl group, an aspect in which both of them are hydrogen atoms, and anaspect in which both of them are alkyl groups (alkyl groups which arethe same as each other or different from each other) are used, and theaspect in which both of them are hydrogen atoms is preferably used. Thepoint described above is also applied to R³ and R⁴ in Formula B in thesame manner.

Ethyleneimine has a structure having the minimum number of carbon atomsconfiguring a ring as alkyleneimine, and the number of carbon atoms of amain chain of the alkyleneimine chain (ethyleneimine chain) obtained byring opening of ethyleneimine is 2. Accordingly, the lower limit of a1in Formula A and a2 in Formula B is 2. That is, a1 in Formula A and a2in Formula B each independently represent an integer equal to or greaterthan 2. a1 in Formula A and a2 in Formula B are each independentlypreferably equal to or smaller than 10, more preferably equal to orsmaller than 6, even more preferably equal to or smaller than 4, stillmore preferably 2 or 3, and still even more preferably 2, from aviewpoint of adhesiveness of the ferromagnetic powder to the surface ofthe particles.

The details of the bonding between the alkyleneimine chain representedby Formula A or the alkyleneimine chain represented by Formula B and thepolyester chain are as described above.

Each alkyleneimine chain is bonded to an adjacent alkyleneimine chain, ahydrogen atom, or a substituent, at a position represented by * in eachFormula. As the substituent, for example, a monovalent substituent suchas an alkyl group (for example, an alkyl group having 1 to 6 carbonatoms) can be used, but there is no limitation. In addition, thepolyester chain may be bonded as the substituent.

Weight-Average Molecular Weight of Polyalkyleneimine Derivative

A molecular weight of the polyalkyleneimine derivative is preferably1,000 to 80,000 as the weight-average molecular weight as describedabove. The weight-average molecular weight of the polyalkyleneiminederivative is more preferably equal to or greater than 1,500, even morepreferably equal to or greater than 2,000, and further more preferablyequal to or greater than 3,000. In addition, the weight-averagemolecular weight of the polyalkyleneimine derivative is more preferablyequal to or smaller than 60,000, even more preferably equal to orsmaller than 40,000, and further more preferably equal to or smallerthan 35,000, and still more preferably equal to or smaller than 34,000.For measurement conditions of the weight-average molecular weight of thepolyalkyleneimine derivative, a specific example which will be describedlater can be referred to.

Synthesis Method

The synthesis method is not particularly limited, as long as thepolyalkyleneimine derivative includes the polyester chain and thepolyalkyleneimine chain having a number average molecular weight of 300to 3,000 at the ratio described above. As a preferred aspect of thesynthesis method, descriptions disclosed in paragraphs 0061 to 0069 ofJP2015-28830A can be referred to.

As a specific example of the polyalkyleneimine derivative, variouspolyalkyleneimine derivatives shown in Table 2 synthesized by usingpolyethyleneimine and polyester shown in Table 2 can be used. For thedetails of the synthesis reaction, descriptions disclosed in Exampleswhich will be described later and/or Examples of JP2015-28830A can bereferred to.

TABLE 2 Percentage of Polyalkyleneimine Polyalkyleneimine chain AmineWeight-average (polyethyleneimine) Polyethyleneimine (polyethyleneiminechain) Acid value value molecular derivative Polyethyleneimine* amount(g) (mass %) Polyester (mgKOH/g) (mgKOH/g) weight (J-1) SP-018 5 4.8(i-1) 22.2 28.6 15,000 (J-2) SP-006 2.4 2.3 (i-2) 35 17.4 7,000 (J-3)SP-012 4.5 4.3 (i-3) 6.5 21.2 22,000 (J-4) SP-006 5 4.8 (i-4) 4.9 11.834,000 (J-5) SP-003 5 4.8 (i-5) 10.1 15.2 19,000 (J-6) SP-018 1.2 1.2(i-6) 68.5 22.4 8,000 (J-7) SP-018 3 2.9 (i-7) 39.9 16.8 13,000 (J-8)SP-012 2.5 2.4 (i-8) 15.5 18.9 18,000 (J-9) SP-006 5 4.8 (i-9) 11.1 16.822,000 (J-10) SP-003 4 3.8 (i-10) 4.4 14.1 24,000 (J-11) SP-012 0.3 0.3(i-11) 8.1 7.8 28,000 (J-12) SP-018 1 1 (i-1) 28.8 6.7 15,000 (J-13)SP-012 5 4.8 (i-6) 61 28.2 4,000 (J-14) SP-006 2.4 2.3 (i-11) 30 17.46,000 (J-15) SP-006 2.4 2.3 (i-12) 42.8 18.1 6,300 (J-16) SP-006 2.4 2.3(i-13) 43.7 17.9 5,900 (J-17) SP-006 2.4 2.3 (i-14) 42.5 17.1 5,300(J-18) SP-006 2.3 2.4 (i-15) 37.5 19.4 7,300 (J-19) SP-006 2.3 2.4(i-16) 24.6 16 9,800 (J-20) SP-006 2.3 2.4 (i-17) 27.5 26.1 9,300 (J-21)SP-006 2.3 2.4 (i-18) 31.7 8.9 8,900 (J-22) SP-006 2.3 2.4 (i-19) 15.313.9 15,100 (J-23) SP-006 2.3 2.4 (i-20) 38.1 22.4 7,580 (*Note)Polyethyleneimine shown in Table 2 is as described below. SP-003(Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.) numberaverage molecular weight of 300) SP-006 (Polyethyleneimine (manufacturedby Nippon Shokubai Co., Ltd.) number average molecular weight of 600)SP-012 (Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.)number average molecular weight of 1,200) SP-018 (Polyethyleneimine(manufactured by Nippon Shokubai Co., Ltd.) number average molecularweight of 1,800)

The polyester shown in Table 2 is polyester synthesized by thering-opening polymerization of lactone by using lactone and anucleophilic reagent (carboxylic acid) shown in Table 3. For the detailsof the synthesis reaction, descriptions disclosed in Examples which willbe described later and/or Examples of JP2015-28830A can be referred to.

TABLE 3 Amount of Weight-average Number average Number of carboxylicmolecular molecular lactone repeating Polyester Carboxylic acid acid (g)Lactone weight weight units (i-1) n-Octanoic acid 12.6 ε-Caprolactone9,000 7,500 20 (i-2) n-Octanoic acid 16.8 ε-Caprolactone 7,000 5,800 15(i-3) n-Octanoic acid 3.3 L-Lactide 22,000 18,000 60 (i-4) Palmitic acid4.5 ε-Caprolactone 38,000 31,000 100 (i-5) Palmitic acid 12.8δ-Valerolactone 16,000 13,000 40 (i-6) Stearic acid 99.7 ε-Caprolactone2,500 2,000 5 (i-7) Glycol acid 13.3 ε-Caprolactone 4,800 4,000 10 (i-8)12-Hydroxystearic acid 20 δ-Valerolactone 13,000 10,000 30 (i-9)12-Hydroxystearic acid 13.2 ε-Caprolactone 17,000 14,000 40 (i-10)2-Naphthoic acid 3.8 ε-Caprolactone 27,000 22,500 80 (i-11)[2-(2-Methoxyethoxy)ethoxy] acetic acid 15.6 ε-Caprolactone 8,700 6,30015 (i-12) n-Octanoic acid 16.8 Lactide 8,100 4,100 15 (i-13) n-Octanoicacid 17.31 L-Lactide 6,900 3,500 10 (L-Lactide derived) ε-Caprolactone 5(ε-Caprolactone derived) (i-14) n-Octanoic acid 17.31 L-Lactide 6,2003,200 5 (L-Lactide dreived) ε-Caprolactone 10 (ε-Caprolactone derived)(i-15) Nonafluorovaleric acid 30.8 ε-Caprolactone 9,000 7,500 15 (i-16)Heptadecafluorononanoic acid 54.2 ε-Caprolactone 8,000 5,000 15 (i-17)3,5,5-Trimethylhexanoic acid 18.5 ε-Caprolactone 10,000 5,800 15 (i-18)4-Oxovaleric acid 13.6 ε-Caprolactone 7,400 4,100 15 (i-19)[2-(2-Methoxyethoxy)ethoxy] acetic acid 20.8 ε-Caprolactone 15,30011,500 30 (i-20) Benzoic acid 14.3 ε-Caprolactone 7,000 3,000 15

The acid value and amine value described above are determined by apotentiometric method (solvent: tetrahydrofuran/water=100/10 (volumeratio), titrant: 0.01 N (0.01 mol/l), sodium hydroxide aqueous solution(acid value), 0.01 N (0.01 mol/l) hydrochloric acid (amine value)).

The average molecular weight (number average molecular weight andweight-average molecular weight) is acquired by performing referencepolystyrene conversion of a value measured by GPC.

Specific examples of the measurement conditions of the average molecularweights of polyester, polyalkyleneimine, and a polyalkyleneiminederivative are respectively as described below.

Measurement Conditions of Average Molecular Weight of Polyester

Measurement device: HLC-8220 GPC (manufactured by Tosoh Corporation)

Column: TSK gel Super HZ2000/TSK gel Super HZ 4000/TSK gel Super HZ-H(manufactured by Tosoh Corporation)

Eluent: Tetrahydrofuran (THF)

Flow rate: 0.35 mL/min

Column temperature: 40° C.

Detector: differential refractometry (RI) detector

Measurement Conditions of Average Molecular Weight of Polyalkyleneimineand Average Molecular Weight of Polyalkyleneimine Derivative

Measurement device: HLC-8320 GPC (manufactured by Tosoh Corporation)

Column: three TSK gel Super AWM-H (manufactured by Tosoh Corporation)

Eluent: N-methyl-2-pyrrolidone (10 mmol/l of lithium bromide is added asan additive)

Flow rate: 0.35 mL/min

Column temperature: 40° C.

Detector: differential refractometry (RI) detector

The content of the dispersing agent for improving dispersibility of theferromagnetic hexagonal ferrite powder described above is preferably 0.5to 25.0 parts by mass with respect to 100.0 parts by mass of theferromagnetic hexagonal ferrite powder. The content of the dispersingagent is preferably equal to or greater than 0.5 parts by mass, morepreferably equal to or greater than 1.0 part by mass, even morepreferably equal to or greater than 5.0 parts by mass, and still morepreferably equal to or greater than 10.0 parts by mass, with respect to100.0 parts by mass of the ferromagnetic hexagonal ferrite powder, fromviewpoints of improving the dispersibility of the ferromagnetichexagonal ferrite powder and the durability of the magnetic layer.Meanwhile, it is preferable to increase the filling percentage of theferromagnetic hexagonal ferrite powder of the magnetic layer, in orderto improve recording density. From this point, it is preferable that thecontent of the components other than the ferromagnetic hexagonal ferritepowder is relatively low. From the viewpoints described above, thecontent of the dispersing agent for improving dispersibility of theferromagnetic hexagonal ferrite powder is preferably equal to or smallerthan 25.0 parts by mass, more preferably equal to or smaller than 20.0parts by mass, even more preferably equal to or smaller than 18.0 partsby mass, and still more preferably equal to or smaller than 15.0 partsby mass with respect to 100.0 parts by mass of the ferromagnetichexagonal ferrite powder.

Hereinafter, the magnetic tape will be further described in detail.

Magnetic Layer

Ferromagnetic Powder

The magnetic layer includes ferromagnetic hexagonal ferrite powder asthe ferromagnetic powder. As an index of a particle size of theferromagnetic hexagonal ferrite powder, an activation volume can beused. The “activation volume” is a unit of magnetization reversal.Regarding the activation volume described in the invention and thespecification, magnetic field sweep rates of a coercivity Hc measurementpart at time points of 3 minutes and 30 minutes are measured by using anoscillation sample type magnetic-flux meter in an environment of anatmosphere temperature of 23° C.±1° C., and the activation volume is avalue acquired from the following relational expression of Hc and anactivation volume V.Hc=2Ku/Ms{1−[(kT/KuV)In(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant, Ms: saturationmagnetization, k: Boltzmann's constant, T: absolute temperature, V:activation volume, A: spin precession frequency, and t: magnetic fieldreversal time]

It is desired that recording density is increased (high-densityrecording is realized) in the magnetic tape, in accordance with a greatincrease in information content of recent years. As a method forachieving high-density recording, a method of decreasing a particle sizeof ferromagnetic powder included in a magnetic layer and increasing afilling percentage of the ferromagnetic powder of the magnetic layer isused. From this viewpoint, the activation volume of the ferromagnetichexagonal ferrite powder is preferably equal to or smaller than 2,500nm³, more preferably equal to or smaller than 2,300 nm³, and even morepreferably equal to or smaller than 2,000 nm³. Meanwhile, from aviewpoint of stability of magnetization, the activation volume is, forexample, preferably equal to or greater than 800 nm³, more preferablyequal to or greater than 1,000 nm³, and even more preferably equal to orgreater than 1,200 nm³. A percentage of the hexagonal ferrite particleshaving the aspect ratio and the length in the long axis directiondescribed above in all of the hexagonal ferrite particles observed inthe STEM image, can be, for example, equal to or greater than 50%, as apercentage with respect to all of the hexagonal ferrite particlesobserved in the STEM image, based on the particle number. In addition,the percentage can be, for example, equal to or smaller than 95% and canexceed 95%.

As one aspect of the ferromagnetic hexagonal ferrite powder,ferromagnetic hexagonal ferrite powder including Al can be used. It isthought that, the ferromagnetic hexagonal ferrite powder is hardened byincluding Al and contributes to the improvement of strength of themagnetic layer. The Al content of the ferromagnetic hexagonal ferritepowder is preferably equal to or greater than 0.6 mass %, morepreferably equal to or greater than 1.0 mass %, even more preferablyequal to or greater than 2.0 mass %, and still more preferably equal toor greater than 3.0 mass % in terms of Al₂O₃, with respect to 100.0 mass% of the total mass of the ferromagnetic hexagonal ferrite powder. Inaddition, the Al content of the ferromagnetic hexagonal ferrite powderis preferably equal to or smaller than 12.0 mass %, more preferablyequal to or smaller than 10.0 mass %, even more preferably equal to orsmaller than 8.0 mass %, and still more preferably equal to or smallerthan 6.0 mass % in terms of Al₂O₃, with respect to 100.0 mass % of thetotal mass of the ferromagnetic hexagonal ferrite powder.

Al may be present in the particle of the ferromagnetic hexagonal ferritepowder, may be adhered to the surface of the particle, or may be presentin the particle and on the surface thereof.

The Al content of the ferromagnetic hexagonal ferrite powder can becalculated from an Al/Fe ratio acquired by inductively coupled plasma(ICP) analysis. In addition, the Al adhered to the surface of theparticle can be confirmed by one or more analysis methods of: confirmingthat an Al/Fe ratio of a surface layer of a particle acquired by X-rayphotoelectron spectroscopy (XPS) analysis becomes greater than the Al/Feratio acquired by the ICP analysis; observing localization of Al on thesurface layer of the particle in Auger electron spectroscopy (AES)analysis; and confirming a coated film on the surface of the particle ina cross section observation performed by using a transmission electronmicroscope (TEM). It is surmised that Al present on the surface of theparticle is normally in a state of an oxide.

For a preparation method of the ferromagnetic hexagonal ferrite powderincluding Al, description disclosed in paragraphs 0012 to 0030 ofJP2011-225417A can be referred to. According to the preparation methoddisclosed in JP2011-225417A, the ferromagnetic hexagonal ferrite powderin which surfaces of primary particles of hexagonal ferrite particlesare coated with Al can also be obtained by a glass crystallizationmethod. In addition, for the preparation method of the ferromagnetichexagonal ferrite powder including Al, description disclosed in aparagraph 0035 of JP2014-179149A can also be referred to.

For details of ferromagnetic hexagonal ferrite powder, for example,descriptions disclosed in paragraphs 0134 0136 of JP2011-216149A andparagraphs 0013 to 0030 of JP2012-204726A can be referred to.

The content (filling percentage) of the ferromagnetic hexagonal ferritepowder of the magnetic layer is preferably in a range of 50 to 90 mass %and more preferably in a range of 60 to 90 mass %. The component otherthan the ferromagnetic hexagonal ferrite powder of the magnetic layer isat least a binding agent and an abrasive, and one or more kinds ofadditives can be arbitrarily included. The high filling percentage ofthe ferromagnetic hexagonal ferrite powder of the magnetic layer ispreferable, from a viewpoint of improving recording density.

Binding Agent

The magnetic tape includes a binding agent in the magnetic layer. Thebinding agent is one or more kinds of resin. For example, as the bindingagent, a resin selected from a polyurethane resin, a polyester resin, apolyamide resin, a vinyl chloride resin, an acrylic resin obtained bycopolymerizing styrene, acrylonitrile, or methyl methacrylate, acellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin,and a polyvinylalkylal resin such as polyvinyl acetal or polyvinylbutyral can be used alone or a plurality of resins can be mixed witheach other to be used. Among these, a polyurethane resin, an acrylicresin, a cellulose resin, and a vinyl chloride resin are preferable.These resins may be homopolymers or copolymers. These resins can be usedas the binding agent even in the non-magnetic layer and/or a backcoating layer which will be described later. For the binding agentdescribed above, description disclosed in paragraphs 0028 to 0031 ofJP2010-24113A can be referred to. In addition, the binding agent may bea radiation curable resin such as an electron beam-curable resin. Forthe radiation curable resin, descriptions disclosed in paragraphs 0044and 0045 of JP2011-48878A can be referred to.

In addition, a curing agent can be used together with a resin which canbe used as the binding agent. The curing agent is a compound includingat least one and preferably two or more crosslinking functional groupsin one molecule. At least a part of the curing agent is included in themagnetic layer in a state of being reacted (crosslinked) with othercomponents such as the binding agent, by proceeding the curing reactionin the magnetic layer forming step. As the curing agent, polyisocyanateis suitable. For the details of polyisocyanate, descriptions disclosedin paragraphs 0124 and 0125 of JP2011-216149A can be referred to. Theamount of the curing agent used can be, for example, 0 to 80.0 parts bymass with respect to 100.0 parts by mass of the binding agent, and ispreferably 50.0 to 80.0 parts by mass, from a viewpoint of improvementof strength of each layer such as the magnetic layer.

Additives

The magnetic layer includes ferromagnetic hexagonal ferrite powder, abinding agent, and an abrasive, and may further include one or morekinds of additives, if necessary. As the additives, a commerciallyavailable product or an additive prepared by a well-known method can besuitably selected and used according to desired properties.

As specific examples of the additives, the dispersing agent and thecuring agent described above are used. The dispersing agent forimproving dispersibility of the ferromagnetic hexagonal ferrite powdercan also contribute to the improvement of dispersibility of theabrasive. The dispersing agent for improving dispersibility of theabrasive can also contribute to the improvement of dispersibility of theferromagnetic hexagonal ferrite powder. In addition, examples of theadditive which can be included in the magnetic layer include anon-magnetic filler, a lubricant, a dispersing assistant, anantibacterial agent, an antistatic agent, an antioxidant, and carbonblack. The non-magnetic filler is identical to the non-magnetic powder.As the non-magnetic filler, a non-magnetic filler (hereinafter, referredto as a “projection formation agent”) which can function as a projectionformation agent which forms projections suitably protruded from thesurface of the magnetic layer can be used. The projection formationagent is a component which can contribute to the control of frictionproperties of the surface of the magnetic layer. As the projectionformation agent, various non-magnetic powders normally used as aprojection formation agent can be used. These may be inorganic powder ororganic powder. In one aspect, from a viewpoint of homogenization offriction properties, particle size distribution of the projectionformation agent is not polydispersion having a plurality of peaks in thedistribution and is preferably monodisperse showing a single peak. Froma viewpoint of availability of monodisperse particles, the projectionformation agent is preferably inorganic powder. Examples of theinorganic powder include powder of metal oxide, metal carbonate, metalsulfate, metal nitride, metal carbide, and metal sulfide, and powder ofinorganic oxide is preferable. The projection formation agent is morepreferably colloidal particles and even more preferably inorganic oxidecolloidal particles. In addition, from a viewpoint of availability ofmonodisperse particles, the inorganic oxide configuring the inorganicoxide colloidal particles are preferably silicon dioxide (silica). Theinorganic oxide colloidal particles are more preferably colloidal silica(silica colloidal particles). In the invention and the specification,the “colloidal particles” are particles which are not precipitated anddispersed to generate a colloidal dispersion, in a case where 1 g of theparticles is added to 100 mL of at least one organic solvent of at leastmethyl ethyl ketone, cyclohexanone, toluene, or ethyl acetate, or amixed solvent including two or more kinds of the solvent described aboveat an arbitrary mixing ratio. In addition, in another aspect, theprojection formation agent is preferably carbon black. An averageparticle size of the projection formation agent is, for example, 30 to300 nm and is preferably 40 to 200 nm. In addition, from a viewpointthat the projection formation agent can exhibit the functions thereof inmore excellent manner, the content of the projection formation agent ofthe magnetic layer is preferably 1.0 to 4.0 parts by mass and morepreferably 1.5 to 3.5 parts by mass with respect to 100.0 parts by massof the ferromagnetic powder.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tapeincludes a non-magnetic layer including non-magnetic powder and abinding agent between the non-magnetic support and the magnetic layer.The non-magnetic powder used in the non-magnetic layer may be inorganicpowder or organic powder. In addition, carbon black and the like canalso be used. Examples of the inorganic powder include powders of metal,metal oxide, metal carbonate, metal sulfate, metal nitride, metalcarbide, and metal sulfide. These non-magnetic powders can be purchasedas a commercially available product or can be manufactured by awell-known method. For details thereof, descriptions disclosed inparagraphs 0146 to 0150 of JP2011-216149A can be referred to. For carbonblack which can be used in the non-magnetic layer, descriptionsdisclosed in paragraphs 0040 and 0041 of JP2010-24113A can be referredto. The content (filling percentage) of the non-magnetic powder of thenon-magnetic layer is preferably in a range of 50 to 90 mass % and morepreferably in a range of 60 to 90 mass %.

In regards to other details of a binding agent or additives of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

The non-magnetic layer of the invention and the specification alsoincludes a substantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binding agent on a side of the non-magneticsupport opposite to the side including the magnetic layer. The backcoating layer preferably includes any one or both of carbon black andinorganic powder. In regards to the binding agent included in the backcoating layer and various additives which can be arbitrarily included inthe back coating layer, a well-known technology regarding the treatmentof the magnetic layer and/or the non-magnetic layer can be applied.

Non-Magnetic Support

Next, the non-magnetic support (hereinafter, also simply referred to asa “support”) will be described. As the non-magnetic support, well-knowncomponents such as polyethylene terephthalate, polyethylene naphthalate,polyamide, polyamide imide, aromatic polyamide subjected to biaxialstretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or thermaltreatment may be performed with respect to these supports in advance.

Various Thickness

The total thickness of the magnetic layer and the non-magnetic layer ofthe magnetic tape is as described above.

A thickness of the non-magnetic support of the magnetic tape ispreferably 3.00 to 4.50 μm.

A thickness of the magnetic layer can be optimized in accordance withsaturation magnetization quantity of the magnetic head used, a head gaplength, or a band of a recording signal. The thickness of the magneticlayer is normally 0.01 μm to 0.15 μm, and is preferably 0.02 μm to 0.12μm and more preferably 0.03 μm to 0.10 μm, from a viewpoint of realizingrecording at high density. The magnetic layer may be at least singlelayer, the magnetic layer may be separated into two or more layershaving different magnetic properties, and a configuration of awell-known multilayered magnetic layer can be applied. A thickness ofthe magnetic layer in a case where the magnetic layer is separated intotwo or more layers is the total thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.10 to 0.55 μmand is preferably 0.10 to 0.50 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.90 μm and even more preferably in a range of 0.10 to 0.70 μm.

In addition, the total thickness of the magnetic tape is preferablyequal to or smaller than 6.00 μm, more preferably equal to or smallerthan 5.70 μm, and even more preferably equal to or smaller than 5.50 μm,from a viewpoint of improving recording capacity for 1 reel of themagnetic tape cartridge. Meanwhile, the total thickness of the magnetictape is preferably equal to or greater than 1.00 μm, from a viewpoint ofavailability (handling properties) of the magnetic tape.

Manufacturing Method of Magnetic Tape

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magnetic tapecan be used. The steps of preparing a composition for forming each layergenerally include at least a kneading step, a dispersing step, and amixing step provided before and after these steps, if necessary. Eachstep may be divided into two or more stages. All of raw materials usedin the invention may be added at an initial stage or in a middle stageof each step. In addition, each raw material may be separately added intwo or more steps. In the preparation of the magnetic layer formingcomposition, it is preferable that the abrasive and the ferromagnetichexagonal ferrite powder are separately dispersed as described above.For the preparation method of the abrasive liquid and the magneticsolution used in the separate dispersing and the preparation method ofthe magnetic layer forming composition, descriptions disclosed inparagraph 0042 to 0048 of JP2014-179149A can be referred to. Inaddition, in order to manufacture the magnetic tape, a well-knownmanufacturing technology can be used. In the kneading step, an openkneader, a continuous kneader, a pressure kneader, or a kneader having astrong kneading force such as an extruder is preferably used. Thedetails of the kneading processes of these kneaders are disclosed inJP1989-106338A (JP-H01-106338A) and JP1989-79274A (JP-H01-79274A). Inaddition, in order to disperse each layer forming composition, glassbeads and one or more kinds of other dispersion beads can be used as adispersion medium. As such dispersion beads, zirconia beads, titaniabeads, and steel beads which are dispersion beads having high specificgravity are suitable. These dispersion beads are preferably used byoptimizing a particle diameter (bead diameter) and a filling percentageof the dispersion beads. As a dispersion device, a well-known dispersiondevice can be used. As one of means for obtaining a magnetic tape havingcos θ of 0.85 to 1.00, a technology of reinforcing the dispersionconditions (for example, increasing the dispersion time, decreasing thediameter of the dispersion beads used for dispersion and/or increasingthe filling percentage of the dispersion beads, using the dispersingagent, and the like) is also preferable. A preferred aspect regardingthe reinforcing of the dispersion conditions is as described above. Forother details of the manufacturing method of the magnetic tape, forexample, descriptions disclosed in paragraphs 0051 to 0057 ofJP2010-24113A can be referred to. For the orientation process, adescription disclosed in a paragraph 0052 of JP2010-24113A can bereferred to. As one of means for obtaining a magnetic tape having cos θof 0.85 to 1.00, a vertical orientation process is preferably performed.

The magnetic tape according to one aspect of the invention describedabove is normally used to be accommodated and circulated in a magnetictape cartridge, in order to record and reproduce a signal. It ispossible to record a signal to the magnetic tape and reproduce therecorded signal by mounting the magnetic tape cartridge on a drive andallowing the running of the magnetic tape in the drive. In the magnetictape, although the total thickness of the non-magnetic layer and themagnetic layer is equal to or smaller than 0.60 μm, it is possible toprevent a deterioration of electromagnetic conversion characteristicswhile repeating the running in a low temperature and high humidityenvironment.

EXAMPLES

Hereinafter, the invention will be described with reference to Examples.However, the invention is not limited to aspects shown in Examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted. In addition, steps and evaluationsdescribed below are performed in an environment of an atmospheretemperature of 23° C.±1° C., unless otherwise noted.

An average particle size of the powder of the invention and thespecification is a value measured by a method disclosed in paragraphs0058 to 0061 of JP2016-071926A. The measurement of the average particlesize described below was performed by using transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. as the transmissionelectron microscope, and image analysis software KS-400 manufactured byCarl Zeiss as the image analysis software.

Preparation Examples of Ferromagnetic Hexagonal Ferrite Powders 1 and 2

In the method disclosed in Example 1 of JP2011-225417A, an Al adhesionamount was adjusted by changing the amount of Al₂O₃ added to a rawmaterial mixture, a particle size was adjusted by changing acrystallization temperature, and ferromagnetic hexagonal ferrite powders1 and 2 (barium ferrite powders) in which Al₂O₃ was adhered to thesurface of the particle were manufactured.

Regarding the manufactured ferromagnetic hexagonal ferrite powders 1 and2, the magnetic field sweep rates of the Hc measurement part at timepoints of 3 minutes and 30 minutes were measured by using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.), and the activation volume was calculated from the relationalexpression described above. In Table 4 below, ferromagnetic hexagonalferrite powder having an activation volume of 2,000 nm³ is theferromagnetic hexagonal ferrite powder 1 and ferromagnetic hexagonalferrite powder having an activation volume of 1,600 nm³ is theferromagnetic hexagonal ferrite powder 2.

In addition, regarding the manufactured ferromagnetic hexagonal ferritepowders 1 and 2, the Al content was measured and the Al presence statewas confirmed by the method disclosed in a paragraph 0070 ofJP2014-179149A. In both of the ferromagnetic hexagonal ferrite powders 1and 2, the Al content was 3.0 mass % in terms of Al₂O₃ with respect to100.0 mass % which is the total mass of the ferromagnetic hexagonalferrite powder used in the measurement. In addition, in both of theferromagnetic hexagonal ferrite powders 1 and 2, it was confirmed thatAl is adhered onto the primary particles (specifically, a coated filmincluding Al is present).

Examples 1 to 9 and Comparative Examples 1 to 10

1. Preparation of Alumina Dispersion (Abrasive Liquid)

2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co.,Ltd.) having the amount shown in Table 4, 31.3 parts of 32% solution(solvent is a mixed solvent of methyl ethyl ketone and toluene) of apolyester polyurethane resin having a SO₃Na group as a polar group(UR-4800 manufactured by Toyobo Co., Ltd. (amount of a polar group: 80meq/kg)), and 570.0 parts of a mixed liquid of methyl ethyl ketone andcyclohexanone at 1:1 (mass ratio) as a solvent were mixed with 100.0parts of alumina powder (Mohs hardness of 9) having a gelatinizationratio of approximately 65% and a BET specific surface area of 20 m²/gshown in Table 4, and dispersed in the presence of zirconia beads by apaint shaker for the time shown in Table 4. After the dispersion, thedispersion liquid and the beads were separated by a mesh and an aluminadispersion (abrasive liquid) was obtained.

2. Magnetic Layer Forming Composition List

Magnetic Solution

Ferromagnetic hexagonal barium ferrite powder (activation volume: seeTable 4): 100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g)

Dispersing agent: see Table 4

Cyclohexanone: 150.0 parts

Methyl ethyl ketone: 150.0 parts

Abrasive liquid

Alumina dispersion prepared in the section 1: 6.0 parts

Silica Sol (Projection Forming Agent Liquid)

Colloidal silica (average particle size of 100 nm): 2.0 parts

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Butyl stearate: 6.0 parts

Polyisocyanate (CORONATE (registered trademark) manufactured by NipponPolyurethane Industry): 2.5 parts

Finishing Additive Solvent

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

The synthesis method or the like of the dispersing agent shown in Table4 will be described later in detail.

3. Non-Magnetic Layer Forming Composition List

Nonmagnetic inorganic powder: α-iron oxide: 100.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

SO₃Na group-containing polyurethane resin: 18.0 parts

(Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g)

Stearic acid: 1.0 part

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

4. Back Coating Layer Forming Composition List

Nonmagnetic inorganic powder: α-iron oxide: 80.0 parts

Average particle size (average long axis length): 0.15 μm

Average acicular ratio: 7

BET specific surface area: 52 m²/g

Carbon black: 20.0 parts

Average particle size: 20 nm

A vinyl chloride copolymer: 13.0 parts

Sulfonic acid salt group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Methyl ethyl ketone: 155.0 parts

Stearic acid: 3.0 parts

Butyl stearate: 3.0 parts

Polyisocyanate: 5.0 parts

Cyclohexanone: 355.0 parts

5. Preparation of Each Layer Forming Composition

(1) Preparation of Magnetic Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

A magnetic solution was prepared by performing beads dispersing of themagnetic solution components described above by using beads as thedispersion medium in a batch type vertical sand mill. Specifically, thedispersing process was performed for the dispersion retention time shownin Table 4 by using zirconia beads having a bead diameter shown in Table4, as the beads dispersion of each stage (first stage, second stage, orthird stage). In the beads dispersion, dispersion liquid obtained byusing filter (average hole diameter of 5 μm) was filtered aftercompletion of each stage. In the beads dispersion of each stage, thefilling percentage of the dispersion medium was set to be approximately50 to 80 volume %.

The magnetic solution obtained as described above was mixed with theabrasive liquid, silica sol, other components, and the finishingadditive solvent and beads-dispersed for the time shown in Table 4 byusing the sand mill, and ultrasonic dispersion was performed with abatch type ultrasonic device (20 kHz, 300 W) for the time shown in Table4. After that, the obtained mixed liquid was filtered by using a filter(average hole diameter: see Table 4), and the magnetic layer formingcomposition was prepared.

A circumferential speed of a tip of the sand mill at the time of beadsdispersion was in a range of 7 to 15 msec.

(2) Preparation of Non-Magnetic Layer Forming Composition

The non-magnetic layer forming composition was prepared by the followingmethod.

Each component excluding stearic acid, cyclohexanone, and methyl ethylketone was beads-dispersed by using a batch type vertical sand mill(dispersion medium: zirconia beads (bead diameter: 0.1 mm), dispersionretention time: 24 hours) to obtain dispersion liquid. After that, theremaining components were added into the obtained dispersion liquid andstirred with a dissolver. Then, the obtained dispersion liquid wasfiltered by using the filter (average hole diameter of 0.5 μm), and anon-magnetic layer forming composition was prepared.

(3) Preparation of Back Coating Layer Forming Composition

The back coating layer forming composition was prepared by the followingmethod.

Each component excluding stearic acid, butyl stearate, polyisocyanate,and cyclohexanone was kneaded and diluted by an open kneader. Then, theobtained mixed liquid was subjected to a dispersing process of 12passes, with a transverse beads mill by using zirconia beads having abead diameter of 1 mm, by setting a bead filling percentage as 80 volume%, a circumferential speed of rotor tip as 10 msec, and a retention timefor 1 pass as 2 minutes. After that, the remaining components were addedinto the obtained dispersion liquid and stirred with a dissolver. Then,the obtained dispersion liquid was filtered with a filter (average holediameter of 1 μm) and a back coating layer forming composition wasprepared.

6. Manufacturing of Magnetic Tape in Which Servo Pattern Is Formed

The non-magnetic layer forming composition prepared in the section 5.(2) was applied to the surface of a support made of polyethylenenaphthalate having a thickness shown in Table 4 so that the thicknessafter the drying becomes the thickness shown in Table 4 and dried, toform a non-magnetic layer. Then, the magnetic layer forming compositionprepared in the section 5. (1) was applied onto the non-magnetic layerso that the thickness after the drying becomes the thickness shown inTable 4. In Examples and Comparative Examples in which “performed” wasshown in the column of the vertical orientation process in Table 4, thevertical orientation process was performed by applying a magnetic fieldhaving a magnetic field strength of 0.3 T to the coating surface in avertical direction, while the coated magnetic layer forming compositionwas not dried, and then, the drying was performed to form the magneticlayer. In Comparative Examples in which “not performed” was shown in thecolumn of the vertical orientation process in Table 4, the coatedmagnetic layer forming composition was dried without performing thevertical orientation process to form the magnetic layer.

After that, the back coating layer forming composition prepared in thesection 5. (3) was applied to the surface of the support made ofpolyethylene naphthalate on a side opposite to the surface where thenon-magnetic layer and the magnetic layer are formed, so that thethickness after the drying becomes the thickness shown in Table 4, anddrying was performed to obtain a laminate.

Then, a surface smoothing treatment (calender process) was performedwith respect to the obtained laminate with a calender roll configured ofonly a metal roll, at a calender process speed of 100 m/min, linearpressure of 294 kN/m (300 kg/cm), and a surface temperature of acalender roll of 95° C.

After that, a thermal treatment was performed in the environment of theatmosphere temperature of 70° C. for 36 hours. The laminate subjected tothe thermal treatment was cut to have a width of ½ inches (0.0127meters) by using a slitter, and a magnetic tape was manufactured.

By performing the steps described above, the magnetic tapes of Examples1 to 9 and Comparative Examples 1 to 10 were manufactured. The thicknessof each layer and the non-magnetic support of the manufactured magnetictape was acquired by the following method. It was confirmed that thethickness of each layer and the non-magnetic support formed is thethickness shown in Table 4.

The cross section of the magnetic tape in a thickness direction wasexposed by an ion beam, and then, the cross section observation of theexposed cross section was performed with a scanning electron microscope.Various thicknesses were acquired as an arithmetical mean of thicknessesacquired at two positions in the thickness direction, in the crosssection observation.

7. Preparation of Dispersing Agent

Dispersing agents 1 to 3 shown in Table 4 used in the magnetic solutionwere prepared by the following method. Hereinafter, a temperature shownregarding the synthesis reaction is a temperature of a reaction liquid.

In Comparative Example 8,2,3-dihydroxynaphthalene was used in themagnetic solution instead of the dispersing agents 1 to 3.2,3-dihydroxynaphthalene is a compound used as an additive of themagnetic layer forming composition, in order to adjust a squarenessratio in JP2012-203955A.

(1) Preparation of Dispersing Agent 1

Synthesis of Precursor 1

197.2 g of ε-caprolactone and 15.0 g of 2-ethyl-1-hexanol wereintroduced into a 500 mL three-neck flask and stirred and dissolvedwhile blowing nitrogen. 0.1 g of monobutyltin oxide was added theretoand heated to 100° C. After 8 hours, the elimination of the raw materialwas confirmed by gas chromatography, the resultant material was cooledto room temperature, and 200 g of a solid precursor 1 (followingstructure) was obtained.

Synthesis of Dispersing Agent 1

40.0 g of the obtained precursor 1 was introduced into 200 mL three-neckflask, and stirred and dissolved at 80° C. while blowing nitrogen. 2.2 gof meso-butane-1,2,3,4-tetracarboxylic dianhydride was added thereto andheated to 110° C. After 5 hours, the elimination of a peak derived fromthe precursor 1 was confirmed by ¹H-NMR, and then, the resultantmaterial was cooled to room temperature, and 38 g of a solid reactionproduct 1 (mixture of the following structural isomer) was obtained. Thereaction product 1 obtained as described above is a mixture of thecompound 1 shown in Table 1 and the structural isomer. The reactionproduct 1 is called a “dispersing agent 1”.

(2) Preparation of Dispersing Agent 2

Synthesis of Dispersing Agent 2

The synthesis was performed in the same manner as in the synthesis ofthe dispersing agent 1, except for changing 2.2 g ofbutanetetracarboxylic acid anhydride and 2.4 g of pyromellitic aciddianhydride, and 38 g of a solid reaction product 2 (mixture of thefollowing structural isomer) was obtained. The reaction product 2obtained as described above is a mixture of the compound 2 shown inTable 1 and the structural isomer. The reaction product 2 is called a“dispersing agent 2”.

(3) Preparation of Dispersing Agent 3

Synthesis of Polyester (i-1)

12.6 g of n-octanoic acid (manufactured by Wako Pure ChemicalIndustries, Ltd.) as carboxylic acid, 100 g of ε-caprolactone (PLACCEL Mmanufactured by Daicel Corporation) as lactone, and 2.2 g of monobutyltin oxide (manufactured by Wako Pure Chemical Industries, Ltd.)(C₄H₉Sn(O)OH) as a catalyst were mixed with each other in a 500 mLthree-neck flask, and heated at 160° C. for 1 hour. 100 g ofε-caprolactone was added dropwise for 5 hours, and further stirred for 2hours. After that, the cooling was performed to room temperature, andpolyester (i-1) was obtained.

The synthesis scheme will be described below.

Synthesis of Dispersing Agent 3 (Polyethyleneimine Derivative (J-1))

5.0 g of polyethyleneimine (SP-018 manufactured by Nippon Shokubai Co.,Ltd., number average molecular weight of 1,800) and 100 g of theobtained polyester (i-1) were mixed with each other and heated at 110°C. for 3 hours, to obtain a polyethyleneimine derivative (J-1). Thepolyethyleneimine derivative (J-1) is called a “dispersing agent 3”.

The synthesis scheme is shown below. In the following synthesis scheme,a, b, c respectively represent a polymerization molar ratio of therepeating unit and is 0 to 50, and a relationship of a+b+c=100 issatisfied. 1, m, n1, and n2 respectively represent a polymerizationmolar ratio of the repeating unit, 1 is 10 to 90, m is 0 to 80, n1 andn2 are 0 to 70, and a relationship of 1+m+n1+n2=100 is satisfied.

The weight-average molecular weight of the dispersing agents 1 and 2 wasmeasured by a method described above as the measurement method of theweight-average molecular weight of the compound represented by GeneralFormula 1. As a result of the measurement, the weight-average molecularweight of the dispersing agent 1 was 9,200 and the weight-averagemolecular weight of the dispersing agent 2 was 6,300.

The weight-average molecular weight of the dispersing agent 3(polyethyleneimine derivative (J-1)) was a value shown in Table 3, whenthe value was acquired by performing reference polystyrene conversion ofa value measured by GPC under the measurement conditions of the specificexample described above.

The weight-average molecular weight other than that described above is avalue acquired by performing reference polystyrene conversion of a valuemeasured by GPC under the following measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm (internal diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

8. State of Abrasive Present in Magnetic Layer (Plan View Maximum AreaPercentage of Abrasive)

By the method described above, the plan view maximum area percentage ofthe abrasive confirmed in a region having a size of 4.3 μm×6.3 μm of thesurface of the magnetic layer is acquired.

9. Measurement of cos θ

A cross section observation sample was cut out from each magnetic tapeof Examples and Comparative Examples, and cos θ was acquired by themethod described above by using this sample. In each magnetic tape ofExamples and Comparative Examples, acquired cos θ is shown in Table 4.In each magnetic tape of Examples and Comparative Examples, a percentageof hexagonal ferrite particles having the aspect ratio and the length inthe long axis direction of the ranges described above which is ameasurement target of cos θ occupying all of the hexagonal ferriteparticles observed in the STEM image, was approximately 80% to 95% basedon the particle number.

The cross section observation sample used for the measurement of cos θwas manufactured by the following method.

(i) Manufacturing of Sample Including Protective Film

A sample including a protective film (laminated film of a carbon filmand a platinum film) was manufactured by the following method.

A sample having a size of a width direction 10 mm×longitudinal direction10 mm of the magnetic tape was cut out from the magnetic tape which is atarget acquiring the cos θ, with a blade. The width direction of thesample described below is a direction which was a width direction of themagnetic tape before the cutting out. The same applies to thelongitudinal direction.

A protective film was formed on the surface of the magnetic layer of thecut-out sample to obtain a sample including a protective film. Theformation of the protective film was performed by the following method.

A carbon film (thickness of 80 nm) was formed on the surface of themagnetic layer of the sample by vacuum deposition, and a platinum (Pt)film (thickness of 30 nm) was formed on the surface of the formed carbonfilm by sputtering. The vacuum deposition of the carbon film and thesputtering of the platinum film were respectively performed under thefollowing conditions.

Vacuum Deposition Conditions of Carbon Film

Deposition source: carbon (core of a mechanical pencil having a diameterof 0.5 mm)

Degree of vacuum in a chamber of a vacuum deposition device: equal to orsmaller than 2×10⁻³ Pa

Current value: 16 A

Sputtering Conditions of Platinum Film

Target: Pt

Degree of vacuum in a chamber of a sputtering device: equal to orsmaller than 7 Pa

Current value: 15 mA

(ii) Manufacturing Cross Section Observation Sample

A sample having a thin film shape was cut out from the sample includinga protective film manufactured in the section (i), by FIB processingusing a gallium ion (Ga⁺) beam. The cutting out was performed byperforming the following FIB processing two times. An accelerationvoltage of the FIB processing was 30 kV.

In a first FIB processing, one end portion (that is, portion includingone side surface of the sample including a protective film in the widthdirection) of the sample including a protective film in the longitudinaldirection, including the area from the surface of the protective film toa region of a depth of approximately 5 μm was cut. The cut-out sampleincludes the area from the protective film to a part of the non-magneticsupport.

Then, a microprobe was loaded on a cut-out surface side (that is, samplecross section side exposed by the cutting out) of the cut-out sample andthe second FIB processing was performed. In the second FIB processing,the surface side opposite to the cut-out surface side (that is, one sidesurface in the width direction) was irradiated with a gallium ion beamto perform the cutting out of the sample. The sample was fixed bybonding the cut-out surface of the second FIB processing to the endsurface of the mesh for STEM observation. After the fixation, themicroprobe was removed.

In addition, the surface of the sample fixed to the mesh, from which themicroprobe is removed, was irradiated with a gallium ion beam at thesame acceleration voltage described above, to perform the FIBprocessing, and the sample fixed to the mesh was further thinned.

The cross section observation sample fixed to the mesh manufactured asdescribed above was observed by a scanning transmission electronmicroscope, and the cos θ was acquired by the method described above.The cos θ acquired as described above is shown in Table 4.

10. Evaluation of Squareness Ratio (SQ)

The squareness ratio of each magnetic tape manufactured was measured ata magnetic field strength of 1194 kA/m(15 kOe) by using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.). The measurement results are shown in Table 4.

11. Change (Decrease of SNR) in Electromagnetic ConversionCharacteristics (Signal-To-Noise-Ratio (SNR)) After Repeated Running inLow Temperature and High Humidity Environment

The electromagnetic conversion characteristics (SNR) were measured bythe following method by using a reel tester having a width of ½ inches(0.0127 meters) and including a fixed head.

A head/tape relative speed was set as 5.5 m/sec, a metal-in-gap (MIG)head (gap length of 0.15 μm, track width of 1.0 μm) was used in therecording, and a recording current was set as an optimal recordingcurrent of each magnetic tape. As a reproducing head, agiant-magnetoresistive (GMR) head having an element thickness of 15 nm,a shield interval 0.1 μm, and a lead width of 0.5 μm was used. Therecording of a signal was performed at linear recording density of 270KFci, and measurement regarding a reproduction signal was performed witha spectrum analyzer manufactured by Shibasoku Co., Ltd. Regarding thesignal, a signal which was sufficiently stabilized after starting therunning of the magnetic tape was used. A ratio of an output value of acarrier signal and integrated noise of the entire spectral range was setas a SNR.

Under the conditions described above, a tape length for 1 pass was setas 1,000 m, the reciprocating running for 5,000 passes was allowed in anenvironment of an atmosphere temperature of 13° C. and relative humidityof 80% to perform reproduction (head/tape relative speed: 6.0 m/sec),and the SNR was measured. A difference between the SNR of the first passand the SNR of the 5,000-th pass (SNR of the 5,000-th pass—SNR of thefirst pass) was acquired. When the difference is less than −2.0 dB, themagnetic tape can be determined as a magnetic tape which shows excellentelectromagnetic conversion characteristics desired in a data back-uptape.

The result described above is shown in Table 4.

TABLE 4 Abrasive liquid Ferro- Abrasive magnetic liquid hexagonalMagnetic solution beads dispersion conditions Abra- dispersing ferriteMagnetic solution First stage Second stage Third stage sive agent (2,3-powder dispersing agent Disper- Bead Disper- Bead Disper- Bead BET Beadsdihydroxy- activation Con- sion reten- diam- sion reten- diam- sionreten- diam- specific dis- naphthalene) volume tent tion time eter tiontime eter tion time eter surface persion Content [nm³] Type [part] [h][mmφ] [h] [mmφ] [h] [mmφ] [m²/g] [h] [part] COMPARATIVE 2000 — — 10 0.5— — — — 20 5 0 EXAMPLE 1 COMPARATIVE 2000 — — 10 0.5 — — — — 20 5 0EXAMPLE 2 COMPARATIVE 2000 — — 10 0.5 — — — — 20 5 0 EXAMPLE 3COMPARATIVE 2000 — — 10 0.5 — — — — 20 5 0 EXAMPLE 4 COMPARATIVE 2000 —— 10 0.5 — — — — 20 5 1 EXAMPLE 5 COMPARATIVE 2000 — — 10 0.5 — — — — 2030 3 EXAMPLE 6 COMPARATIVE 2000 — — 10 0.5 — — — — 30 30 3 EXAMPLE 7COMPARATIVE 2000 2,3- 12.0 10 0.5 10 0.1 — — 20 30 3 EXAMPLE 8dihydroxy- naphthalene COMPARATIVE 2000 Dispersing 6.0 10 0.5 10 0.1 — —20 5 0 EXAMPLE 9 agent 1 COMPARATIVE 2000 Dispersing 6.0 10 0.5 10 0.1 —— 30 30 5 EXAMPLE 10 agent 1 EXAMPLE 1 2000 Dispersing 6.0 10 0.5 10 0.1— — 20 5 1 agent 1 EXAMPLE 2 2000 Dispersing 12.0 10 0.5 30 0.1 — — 20 51 agent 1 EXAMPLE 3 2000 Dispersing 12.0 10 0.5 10 0.1 10 0.05 20 5 1agent 1 EXAMPLE 4 2000 Dispersing 6.0 10 0.5 10 0.1 — — 20 5 1 agent 2EXAMPLE 5 2000 Dispersing 6.0 10 0.5 10 0.1 — — 20 5 1 agent 3 EXAMPLE 62000 Dispersing 6.0 10 0.5 10 0.1 — — 20 30 3 agent 1 EXAMPLE 7 2000Dispersing 6.0 10 0.5 10 0.1 — — 30 30 3 agent 1 EXAMPLE 8 2000Dispersing 6.0 10 0.5 10 0.1 — — 20 30 3 agent 1 EXAMPLE 9 1600Dispersing 6.0 10 0.5 10 0.1 — — 20 30 3 agent 1 Treatment conditionsafter Non- mixing of magnetic solution, mag- abrasive liquid, silicasol, Non- netic other components, and Non- mag- Back layer + finishingadditive solvent Mag- mag- netic coat- mag- Evaluation result Ultra-Filter netic netic sup- ing netic Plan view Beads sonic average Verticallayer layer port layer Total maximum SNR disper- disper- hole orienta-Thick- Thick- Thick- Thick- thick- area per- de- sion time sion timediam- tion ness ness ness ness ness SQ Cosθ centage crease [min] [min]eter process [μm] [μm] [μm] [μm] [μm] [—] [—] of abrasive [dB]COMPARATIVE 5 0.5 0.5 μm Not 0.10 1.00 4.30 0.60 1.10 0.58 0.68 0.06%−0.3 EXAMPLE 1 performed COMPARATIVE 5 0.5 0.5 μm Not 0.10 0.70 4.300.60 0.80 0.58 0.68 0.06% −0.5 EXAMPLE 2 performed COMPARATIVE 5 0.5 0.5μm Not 0.10 0.50 4.30 0.60 0.60 0.58 0.68 0.06% −2.6 EXAMPLE 3 performedCOMPARATIVE 5 0.5 0.5 μm Not 0.10 0.10 4.30 0.60 0.20 0.58 0.68 0.06%−5.4 EXAMPLE 4 performed COMPARATIVE 60 30 0.5 μm Not 0.10 0.50 4.300.60 0.60 0.58 0.68 0.05% −3.7 EXAMPLE 5 performed COMPARATIVE 60 30 0.5μm Not 0.10 0.50 4.30 0.60 0.60 0.58 0.68 0.04% −4.8 EXAMPLE 6 performedCOMPARATIVE 180 60 0.3 μm Not 0.10 0.50 4.30 0.60 0.60 0.58 0.68 0.02%−6.5 EXAMPLE 7 performed COMPARATIVE 60 30 0.5 μm Performed 0.10 0.504.30 0.60 0.60 0.78 0.80 0.04% −3.1 EXAMPLE 8 COMPARATIVE 5 0.5 0.5 μmPerformed 0.10 0.50 4.30 0.60 0.60 0.73 0.87 0.06% −6.0 EXAMPLE 9COMPARATIVE 360 60 0.3 μm Performed 0.10 0.50 4.30 0.60 0.60 0.73 0.870.01% −2.3 EXAMPLE 10 EXAMPLE 1 60 30 0.5 μm Performed 0.10 0.50 4.300.60 0.60 0.73 0.87 0.05% −0.7 EXAMPLE 2 60 30 0.5 μm Performed 0.100.50 4.30 0.60 0.60 0.74 0.96 0.05% −0.3 EXAMPLE 3 60 30 0.5 μmPerformed 0.10 0.50 4.30 0.60 0.60 0.74 0.98 0.05% −0.2 EXAMPLE 4 60 300.5 μm Performed 0.10 0.50 4.30 0.60 0.60 0.73 0.87 0.05% −0.7 EXAMPLE 560 30 0.5 μm Performed 0.10 0.50 4.30 0.60 0.60 0.73 0.85 0.05% −0.8EXAMPLE 6 60 30 0.5 μm Performed 0.10 0.50 4.30 0.60 0.60 0.73 0.870.04% −0.5 EXAMPLE 7 180 60 0.3 μm Performed 0.10 0.50 4.30 0.60 0.600.73 0.87 0.02% −0.6 EXAMPLE 8 60 30 0.5 μm Performed 0.10 0.10 4.300.60 0.20 0.73 0.87 0.04% −0.4 EXAMPLE 9 60 30 0.5 μm Performed 0.100.50 4.30 0.60 0.60 0.72 0.86 0.04% −0.5

With the comparison of Comparative Examples, it was confirmed that, inthe case where the total thickness of the non-magnetic layer and themagnetic layer is equal to or smaller than 0.60 μm (Comparative Examples3 to 10), the SNR is significantly decreased by the repeated running ina low temperature and high humidity environment, compared to the casewhere the total thickness of the non-magnetic layer and the magneticlayer exceeds 0.60 μm (Comparative Examples 1 and 2).

When a reproducing head after evaluation of the magnetic tape of each ofComparative Examples was visually observed, in a reproducing head ofComparative Examples 3, 4, and 9 after the evaluation, it was confirmedthat a phenomenon called pole tip recession (PTR) in which a differencein level of an element portion and a sliding surface of a GMR headoccurs. It is assumed that the PTR is generated due to the chipping ofthe element part of the GMR head caused by the sliding on the surface ofthe magnetic layer. Meanwhile, in the reproducing head of ComparativeExamples 5 to 8 and 10 after the evaluation, it was confirmed thatforeign materials were attached to the GMR head. It is considered that,when the abrasion properties of the surface of the magnetic layer arenot sufficiently exhibited, the head attached materials are not removed.

With respect to this, in the magnetic tape of Examples 1 to 9, the totalthickness of the non-magnetic layer and the magnetic layer was equal toor smaller than 0.60 μm, but a decrease in SNR was prevented, comparedto the magnetic tape of Comparative Examples 3 to 10.

From the results shown in Table 4, an excellent correlation can beconfirmed between the cos θ and a degree of the decrease of SNR, in thatas the value of cos θ increases, the decrease of SNR is prevented (forexample, see Examples 1 to 5 in which the plan view maximum areapercentage of the abrasive is the same value). With respect to this,such a correlation was not observed between the squareness ratio (SQ)and a degree of the decrease of SNR, as shown in Table 4.

The invention is effective in technical fields of magnetic tapes forhigh-density recording.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; a non-magnetic layer including non-magnetic powder and abinding agent on the non-magnetic support; and a magnetic layerincluding ferromagnetic powder and a binding agent on the non-magneticlayer, wherein the total thickness of the non-magnetic layer and themagnetic layer is equal to or smaller than 0.60 μm, the ferromagneticpowder is ferromagnetic hexagonal ferrite powder, the magnetic layerincludes an abrasive, the percentage of a plan view maximum area of theabrasive confirmed in a region having a size of 4.3 μm×6.3 μm of thesurface of the magnetic layer by plane observation using a scanningelectron microscope, with respect to the total area of the region isequal to or greater than 0.02% and less than 0.06%, the tilt cos θ ofthe ferromagnetic hexagonal ferrite powder with respect to a surface ofthe magnetic layer acquired by cross section observation performed byusing a scanning transmission electron microscope is 0.85 to 1.00, andthe percentage of hexagonal ferrite particles having a length in thelong axis direction of equal to or greater than 10 nm and having anaspect ratio in a range of 1.5 to 6.0 in all of the hexagonal ferriteparticles is equal to or greater than 50% but equal to or smaller than95%, based on the particle number.
 2. The magnetic tape according toclaim 1, wherein a BET specific surface area of the abrasive is in arange of 14 to 40 m²/g.
 3. The magnetic tape according to claim 1,wherein the abrasive is alumina powder.
 4. The magnetic tape accordingto claim 2, wherein the abrasive is alumina powder.
 5. The magnetic tapeaccording to claim 1, wherein the cos θ is 0.89 to 1.00.
 6. The magnetictape according to claim 1, wherein the cos θ is 0.95 to 1.00.
 7. Themagnetic tape according to claim 2, wherein the cos θ is 0.89 to 1.00.8. The magnetic tape according to claim 2, wherein the cos θ is 0.95 to1.00.
 9. The magnetic tape according to claim 3, wherein the cos θ is0.89 to 1.00.
 10. The magnetic tape according to claim 3, wherein thecos θ is 0.95 to 1.00.
 11. The magnetic tape according to claim 4,wherein the cos θ is 0.89 to 1.00.
 12. The magnetic tape according toclaim 4, wherein the cos θ is 0.95 to 1.00.
 13. The magnetic tapeaccording to claim 1, wherein the magnetic layer includes a polyesterchain-containing compound having a weight-average molecular weight of1,000 to 80,000.
 14. The magnetic tape according to claim 1, wherein theactivation volume of the ferromagnetic hexagonal ferrite powder is 800nm³ to 2,500 nm³.
 15. The magnetic tape according to claim 1, whereinthe percentage of a plan view maximum area of the abrasive confirmed ina region having a size of 4.3 μm×6.3 μm of the surface of the magneticlayer by plane observation using a scanning electron microscope, withrespect to the total area of the region is 0.02% to 0.05%.
 16. Themagnetic tape according to claim 1, wherein the total thickness of thenon-magnetic layer and the magnetic layer is 0.20 μm to 0.60 μm.
 17. Themagnetic tape according to claim 1, wherein the magnetic layer includesan aromatic hydrocarbon compound including a phenolic hydroxyl group.18. The magnetic tape according to claim 1, wherein the ferromagnetichexagonal ferrite powder includes Al.
 19. The magnetic tape according toclaim 1, wherein the tilt cos θ is 0.85 to 0.98.